To provide a durable, unexpensive check valve capable of maintaining a function for preventing a backward flow for a long term.

The check valve comprises a valve body 3 which is placed in a movable state in a controlled space 2 formed in a part of a pipe 1, a valve seat 5 having a valve port 4 which is blocked by forming an end of the controlled space 2 and by sticking the valve body 3, and a stopper 6 constituting the control space 2 together with the value seat 5 and controlling a movable range of the valve body 3 while the valve port 4 is open. Hardness of at least a contact portion on the valve body 3 is lower than that of at least a contact portion on the valve seat 5 and the stopper 6.