Abstract: Disclosed is an improved hydraulic lash adjustor in a valve operating mechanism for automatically eliminating valve head clearance of the type which includes a cylinder, a plunger slidably fitted into the cylinder and a check valve accommodated in a valve cage secured to the bottom portion of the plunger, said check valve being adapted to control communication between a hydraulic chamber defined below the plunger and a hydraulic oil reservoir chamber formed in the plunger in dependence on operation of an engine. A flange portion of the valve cage is firmly held in position between the bottom portion of the plunger and a caulking ring fitted into an annular engagement groove formed on the plunger. The annular engagement groove has upper and lower side wall surfaces and at least the lower side wall surface is formed as a tapered face which extends radially inward at a downward inclination angle.