A hydraulic tensioner (1) that decreases the number of components, secures an adequate backlash, and prevents backward movement of a plunger (3). The hydraulic tensioner (1) includes a hollow plunger (3) having rack teeth (3b) formed on a portion of an outer circumferential surface, slidably received in a bore (2a) of the housing (2), where the plunger (3) has an inner space to form a fluid chamber with the bore. A slider (72) housing portion, having an inclined surface, located in the housing (2), receives a wedge-shaped slider (72) having a ratchet portion (72a) adapted to engage with the rack teeth (3b) of the plunger (3) and a second side surface. The wedge-shaped slider (72) being slidable along the inclined surface of the slider housing portion in a direction crossing an axial centerline of the plunger (3). The hydraulic tensioner (1) further includes a first spring (4) biasing the plunger (3) in a protruding direction, and a second spring (73) biasing the slider (72) such that the slider moves along the inclined slide surface of the slider housing portion. A "wedge-effect" prevents the plunger (3) from moving backwards.