An object is to provide an oil feed type auto-tensioner which can reliably prevent air from mixing into hydraulic oil in the pressure chamber.This tensioner includes a housing (11) defining a cylinder chamber (13), a plunger (14) slidably mounted in the cylinder chamber (13), a return spring (15) mounted in the cylinder chamber (13) and biasing the plunger (14) outwardly of the cylinder chamber (13), the housing (11) being formed with an oil supply passage (17) communicating with a pressure chamber (16) defined in the cylinder chamber behind the plunger (14), and a check valve (18) provided at a hydraulic oil outlet of the oil supply passage (17). The cylinder chamber (13) includes a large-diameter hole portion (19) provided at an open end thereof, in which a snap ring (20) for braking is received so as to be movable therein. The snap ring (20) includes a plurality of engaging pieces (20a) provided at a radially inner portion thereof and inclined in a direction in which the plunger (14) protrudes from the housing. The engaging pieces (20a) have radially inner edges that are in engagement with the outer periphery of the plunger, thereby restraining retraction of the plunger. When a pushing force is applied to the plunger (14) from the chain while the engine is at a stop, the snap ring (20) for braking abuts the closed end face of the large-diameter hole portion (19) and is stopped. In this state, because the radially inner edges of the engaging pieces (20a) formed on the radially inner portion of the snap ring (20) are in engagement with the outer periphery of the plunger (14), the plunger (14) is prevented from retracting, thus keeping the tension of the chain within a predetermined range. This prevents the plunger (14) from markedly moving outwardly when the engine is subsequently restarted.