Provided is a hydraulic lash adjuster which can, when an internal combustion engine is being stopped, retain a large amount of hydraulic oil in a reservoir communicating with a high-pressure chamber. A hydraulic lash adjuster is provided with a body (24) open in the upper part thereof, and also with a plunger (26) in sliding contact with the inner peripheral surface of the body (24) to define a high-pressure chamber (29) at the bottom of the plunger (26) and having an upper end functioning as an operating end. The plunger (26) is provided with a reservoir (28) communicating with an external oil path (32) through an oil supply hole (27a) formed in a side wall of the plunger (26) and through an oil supply hole (24b) formed in a side wall of the body (24). A check valve (40A) for opening theoil supply hole (24b) by the pressure of hydraulic oil led from the external oil path (32) to the oil supply path (24b) is formed in an annular communicating path (T) provided between the side wall of the plunger (26) and the side wall of the body (24) and interconnecting the oil supply hole (27a) and the oil supply hole (24b). When the engine is being operated, a recycle action of leak-down oil is performed. When the engine is being stopped, the check valve (40A) closes the oil supply hole (24b), and as a result, the level (H) of the hydraulic oil in the reservoir (28) communicating with thehigh-pressure chamber (29) does not descend to a level equal to or lower than an opening end of the body (24), which enables a large amount of hydraulic oil to be retained in the reservoir (28).