<p>A chain tensioner (1) in which a plunger (12) is slidably assembled in a cylinder part (13) together with a return spring (11). The chain tensioner includes a stopper plate (22) provided with a through hole (22a) through which a plunger (12) is inserted, and a biasing member (24) for disabling the plunger (12) from its movement by imparting a biasing force to the end of the stopper plate (22) to tilt the stopper plate (22). The movement of the plunger (12) can be allowed by applying the hydraulic pressure of hydraulic oil for an engine onto the stopper plate (22) to reduce the inclination of the stopper plate (22) against the biasing force of the biasing member (24).</p>
