<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) in which a through hole (22a) for inserting the plunger (12) therethrough is formed, and a biasing member (24) for disabling movement of the plunger (12) by imparting a biasing force to the end of the stopper plate (22) so as to tilt the stopper plate (22). Hydraulic pressure of the hydraulic oil for an engine act on the stopper plate (22) whereby the inclination of the stopper plate (22) is reduced against the biasing force of the biasing member (24), and thereby, the movement of the plunger (12) can be permitted.</p>
