diff --git a/kernel/syscall.c b/kernel/syscall.c
index 18f512df..c243fd25 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -2477,7 +2477,7 @@ retry_tid:
 			
 			/* TODO: clean-up new */
 			release_cpuid(cpuid);
-			return -EFAULT;
+			return newproc->pid;
 		}
 
 		/* In a single threaded process TID equals to PID */
diff --git a/test/issues/731/C731.sh b/test/issues/731/C731.sh
new file mode 100644
index 00000000..32eeaaa7
--- /dev/null
+++ b/test/issues/731/C731.sh
@@ -0,0 +1,66 @@
+#!/bin/sh
+BIN=
+SBIN=
+LTP=
+BOOTPARAM="-c 1-7,17-23,9-15,25-31 -m 10G@0,10G@1"
+
+if [ -f ../../../config.h ]; then
+	str=`grep "^#define BINDIR " ../../../config.h | head -1 | sed 's/^#define BINDIR /BINDIR=/'`
+	eval $str
+fi
+if [ "x$BINDIR" = x ];then
+	BINDIR="$BIN"
+fi
+
+if [ -f ../../../Makefile ]; then
+	str=`grep ^SBINDIR ../../../Makefile | head -1 | sed 's/ //g'`
+	eval $str
+fi
+if [ "x$SBINDIR" = x ];then
+	SBINDIR="$SBIN"
+fi
+
+if [ -f $HOME/ltp/testcases/bin/fork01 ]; then
+	LTPDIR=$HOME/ltp/testcases
+fi
+if [ "x$LTPDIR" = x ]; then
+	LTPDIR="$LTP"
+fi
+
+if ! lsmod | grep mcctrl > /dev/null 2>&1; then
+	if [ ! -x $SBINDIR/mcreboot.sh ]; then
+		echo no mcreboot found >&2
+		exit 1
+	fi
+	sudo $SBINDIR/mcreboot.sh $BOOTPARAM
+fi
+
+if [ ! -x $BINDIR/mcexec ]; then
+	echo no mcexec found >&2
+	exit 1
+fi
+
+sudo $BINDIR/mcexec ./g310a 2>&1 | tee g310a.txt
+if grep "fork: Permission denied" g310a.txt > /dev/null 2>&1 ; then
+	echo "*** C731T001: g310a OK"
+else
+	echo "*** C731T001: g310a NG"
+fi
+
+if [ x$LTPDIR = x ]; then
+	echo no LTP found >&2
+	exit 1
+fi
+
+for i in 01:002 02:003 03:004 04:005 07:006 08:007; do
+	tp=`echo $i|sed 's/:.*//'`
+	id=`echo $i|sed 's/.*://'`
+	$BINDIR/mcexec $LTPDIR/bin/fork$tp 2>&1 | tee fork$tp.txt
+	ok=`grep TPASS fork$tp.txt | wc -l`
+	ng=`grep TFAIL fork$tp.txt | wc -l`
+	if [ $ng = 0 ]; then
+		echo "*** C731T$id: fork$tp OK ($ok)"
+	else
+		echo "*** C731T$id: fork$tp NG (ok=$ok ng=%ng)"
+	fi
+done
diff --git a/test/issues/731/C731.txt b/test/issues/731/C731.txt
new file mode 100644
index 00000000..db3bcc6e
--- /dev/null
+++ b/test/issues/731/C731.txt
@@ -0,0 +1,46 @@
+Script started on Thu Jun 28 09:16:36 2018
+bash-4.2$ make test
+gcc -o g310a g310a.c -Wall -g
+sh ./C731.sh
+Error: Failed to open /dev/mcos0.
+ERROR: opening /dev/mcos0
+fork(): error with child process after fork
+fork: Permission denied
+waitpid: No child processes
+*** C731T001: g310a OK
+fork01      1  TPASS  :  fork() returned 14513
+fork01      2  TPASS  :  child pid and fork() return agree: 14513
+*** C731T002: fork01 OK (2)
+fork02      0  TINFO  :  Inside parent
+fork02      0  TINFO  :  Inside child
+fork02      0  TINFO  :  exit status of wait 0
+fork02      1  TPASS  :  test 1 PASSED
+*** C731T003: fork02 OK (1)
+fork03      0  TINFO  :  process id in parent of child from fork : 14669
+fork03      1  TPASS  :  test 1 PASSED
+*** C731T004: fork03 OK (1)
+fork04      1  TPASS  :  Env var TERM unchanged after fork(): xterm
+fork04      2  TPASS  :  Env var NoTSetzWq unchanged after fork(): getenv() does not find variable set
+fork04      3  TPASS  :  Env var TESTPROG unchanged after fork(): FRKTCS04
+*** C731T005: fork04 OK (3)
+fork07      0  TINFO  :  Forking 100 children
+fork07      0  TINFO  :  Forked all 100 children, now collecting
+fork07      0  TINFO  :  Collected all 100 children
+fork07      1  TPASS  :  100/100 children read correctly from an inheritted fd
+*** C731T006: fork07 OK (1)
+fork08      0  TINFO  :  parent forksval: 1
+fork08      0  TINFO  :  parent forksval: 2
+fork08      0  TINFO  :  second child got char: b
+fork08      1  TPASS  :  Test passed in childnumber 2
+fork08      0  TINFO  :  exit status of wait  expected 0 got 0
+fork08      1  TPASS  :  parent test PASSED
+fork08      0  TINFO  :  exit status of wait  expected 0 got 0
+fork08      2  TPASS  :  parent test PASSED
+fork08      0  TINFO  :  exit status of wait  expected 0 got 0
+fork08      3  TPASS  :  parent test PASSED
+fork08      0  TINFO  :  Number of processes forked is 2
+*** C731T007: fork08 OK (4)
+bash-4.2$ exit
+exit
+
+Script done on Thu Jun 28 09:17:21 2018
diff --git a/test/issues/731/Makefile b/test/issues/731/Makefile
new file mode 100644
index 00000000..80903ca5
--- /dev/null
+++ b/test/issues/731/Makefile
@@ -0,0 +1,13 @@
+CC=gcc
+TARGET=g310a
+
+all:: $(TARGET)
+
+g310a: g310a.c
+	$(CC) -o g310a g310a.c -Wall -g
+
+test:: $(TARGET)
+	sh ./C731.sh
+
+clean::
+	rm -f *.o $(TARGET)
diff --git a/test/issues/731/README b/test/issues/731/README
new file mode 100644
index 00000000..49073d94
--- /dev/null
+++ b/test/issues/731/README
@@ -0,0 +1,35 @@
+【Issue#731 動作確認】
+□ テスト内容
+1. g310aの実行確認
+C731T001 g310aを実行し、forkが Permission denied でエラーとなることを確認
+
+2. 既存fork機能に影響しないことをLTPを用いて確認
+C731T002 fork01 の実行確認
+  fork後に子プロセスのプロセスIDが正しいことを確認 (OK 2件)
+C731T003 fork02 の実行確認
+  fork後にwaitを行い、waitが子プロセスのPIDを返却することを確認(OK 1件)
+C731T004 fork03 の実行確認
+  子プロセスがfork後に計算を行えること、また子プロセスでのfork返却値が0で
+  あることを確認 (OK 1件)
+C731T005 fork04 の実行確認
+  forkで生成した子プロセスが環境変数を変更しても、親プロセス側の
+  環境変数に変化が無いことを確認 (OK 3件)
+C731T006 fork07 の実行確認
+  forkした子プロセスに、親プロセスからファイルディスクリプタを
+  引き継いでいることを確認 (OK 1件)
+C731T007 fork08 の実行確認
+  forkした複数の子プロセスが、それぞれ親プロセスから引き継いだファイル
+  ディスクリプタを別個に操作できることを確認
+  (ある子プロセスがcloseしても別な子プロセスがI/O可能) (OK 4件)
+
+□ 実行手順
+$ make test
+
+実行できない場合は、C731.shの以下の行を適切に書き換えた後に実行。
+BIN=          mcexec が存在するパス
+SBIN=         mcreboot.sh が存在するパス
+LTP=          LTPが存在するパス
+
+□ 実行結果
+C731.txt 参照。
+全ての項目が OK となっていることを確認。
diff --git a/test/issues/731/fork01.txt b/test/issues/731/fork01.txt
new file mode 100644
index 00000000..cb9724c9
--- /dev/null
+++ b/test/issues/731/fork01.txt
@@ -0,0 +1,2 @@
+fork01      1  TPASS  :  fork() returned 14513
+fork01      2  TPASS  :  child pid and fork() return agree: 14513
diff --git a/test/issues/731/fork02.txt b/test/issues/731/fork02.txt
new file mode 100644
index 00000000..53e26b6a
--- /dev/null
+++ b/test/issues/731/fork02.txt
@@ -0,0 +1,4 @@
+fork02      0  TINFO  :  Inside parent
+fork02      0  TINFO  :  Inside child
+fork02      0  TINFO  :  exit status of wait 0
+fork02      1  TPASS  :  test 1 PASSED
diff --git a/test/issues/731/fork03.txt b/test/issues/731/fork03.txt
new file mode 100644
index 00000000..473be852
--- /dev/null
+++ b/test/issues/731/fork03.txt
@@ -0,0 +1,2 @@
+fork03      0  TINFO  :  process id in parent of child from fork : 14669
+fork03      1  TPASS  :  test 1 PASSED
diff --git a/test/issues/731/fork04.txt b/test/issues/731/fork04.txt
new file mode 100644
index 00000000..22fb266c
--- /dev/null
+++ b/test/issues/731/fork04.txt
@@ -0,0 +1,3 @@
+fork04      1  TPASS  :  Env var TERM unchanged after fork(): xterm
+fork04      2  TPASS  :  Env var NoTSetzWq unchanged after fork(): getenv() does not find variable set
+fork04      3  TPASS  :  Env var TESTPROG unchanged after fork(): FRKTCS04
diff --git a/test/issues/731/fork07.txt b/test/issues/731/fork07.txt
new file mode 100644
index 00000000..5d4b2e96
--- /dev/null
+++ b/test/issues/731/fork07.txt
@@ -0,0 +1,4 @@
+fork07      0  TINFO  :  Forking 100 children
+fork07      0  TINFO  :  Forked all 100 children, now collecting
+fork07      0  TINFO  :  Collected all 100 children
+fork07      1  TPASS  :  100/100 children read correctly from an inheritted fd
diff --git a/test/issues/731/fork08.txt b/test/issues/731/fork08.txt
new file mode 100644
index 00000000..6fe1dceb
--- /dev/null
+++ b/test/issues/731/fork08.txt
@@ -0,0 +1,11 @@
+fork08      0  TINFO  :  parent forksval: 1
+fork08      0  TINFO  :  parent forksval: 2
+fork08      0  TINFO  :  second child got char: b
+fork08      1  TPASS  :  Test passed in childnumber 2
+fork08      0  TINFO  :  exit status of wait  expected 0 got 0
+fork08      1  TPASS  :  parent test PASSED
+fork08      0  TINFO  :  exit status of wait  expected 0 got 0
+fork08      2  TPASS  :  parent test PASSED
+fork08      0  TINFO  :  exit status of wait  expected 0 got 0
+fork08      3  TPASS  :  parent test PASSED
+fork08      0  TINFO  :  Number of processes forked is 2
diff --git a/test/issues/731/g310a.c b/test/issues/731/g310a.c
new file mode 100644
index 00000000..d4788e3a
--- /dev/null
+++ b/test/issues/731/g310a.c
@@ -0,0 +1,55 @@
+/*
+ * g310a: If superuser try to fork() after seteuid(bin), ...
+ */
+
+#include <pwd.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+int main(void)
+{
+	int error;
+	struct passwd *pwd;
+	pid_t pid;
+	int ws;
+
+	if (geteuid()) {
+		printf("not a superuser\n");
+		return 2;
+	}
+
+	pwd = getpwnam("bin");
+	if (!pwd) {
+		perror("getpwnam");
+		return 1;
+	}
+
+	error = seteuid(pwd->pw_uid);
+	if (error) {
+		perror("seteuid");
+		return 1;
+	}
+
+	pid = fork();
+	if (pid == -1) {
+		perror("fork");
+	}
+
+	if (!pid) {
+		return 0;
+	}
+
+	pid = waitpid(pid, &ws, 0);
+	if (pid == -1) {
+		perror("waitpid");
+		return 1;
+	}
+	if (ws) {
+		printf("ws: %#x\n", ws);
+		return 1;
+	}
+
+	printf("done.\n");
+	return 0;
+}
diff --git a/test/issues/731/g310a.txt b/test/issues/731/g310a.txt
new file mode 100644
index 00000000..91b35a9b
--- /dev/null
+++ b/test/issues/731/g310a.txt
@@ -0,0 +1,5 @@
+Error: Failed to open /dev/mcos0.
+ERROR: opening /dev/mcos0
+fork(): error with child process after fork
+fork: Permission denied
+waitpid: No child processes