diff --git a/ChangeLog b/ChangeLog
index 88de5db..31fb448 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2020-06-23  NIIBE Yutaka  <gniibe@fsij.org>
+
+	* chopstx.c (chopstx_critical): New.
+
 2019-12-27  NIIBE Yutaka  <gniibe@fsij.org>
 
 	* contrib/spi-st.c (check_transmit, put_data): Fix handling
diff --git a/chopstx.c b/chopstx.c
index 15f0a5e..551bf71 100644
--- a/chopstx.c
+++ b/chopstx.c
@@ -1,7 +1,7 @@
 /*
  * chopstx.c - Threads and only threads.
  *
- * Copyright (C) 2013, 2014, 2015, 2016, 2017, 2018, 2019
+ * Copyright (C) 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020
  *               Flying Stone Technology
  * Author: NIIBE Yutaka <gniibe@fsij.org>
  *
@@ -1700,3 +1700,23 @@ chopstx_conf_idle (int enable_sleep)
 
   return r;
 }
+
+
+/**
+ * chopstx_critical - Construct a critical section
+ * @func: function to be called
+ * @arg: argument to function
+ *
+ * Run the function @func with @arg under CPU schedule lock.
+ * Return void * pointer.
+ */
+void *
+chopstx_critical (void *func (void *), void *arg)
+{
+  void *p;
+
+  chx_cpu_sched_lock ();
+  p = func (arg);
+  chx_cpu_sched_unlock ();
+  return p;
+}
diff --git a/chopstx.h b/chopstx.h
index 45d7320..1342203 100644
--- a/chopstx.h
+++ b/chopstx.h
@@ -1,7 +1,8 @@
 /*
  * chopstx.h - Threads and only threads.
  *
- * Copyright (C) 2013, 2016, 2017, 2018  Flying Stone Technology
+ * Copyright (C) 2013, 2016, 2017, 2018, 2020
+ *               Flying Stone Technology
  * Author: NIIBE Yutaka <gniibe@fsij.org>
  *
  * This file is a part of Chopstx, a thread library for embedded.
@@ -161,3 +162,5 @@ int chopstx_poll (uint32_t *usec_p, int n,
 		  struct chx_poll_head *const pd_array[]);
 
 int chopstx_conf_idle (int enable_sleep);
+
+void *chopstx_critical (void *func (void *), void *arg);