To prevent a crack and extension at the time of press-in, by respectively specifying the opening angles of retaining claws of a cap retainer, which are mounted as parts for a lash adjuster by which the clearance of a valve is automatically adjusted, and an angle between the retaining claws which adjoin each other.

In a cap retainer 1, a retaining claw 8 is pressed into a lash adjuster body 10 from the upper part of a plunger cap so as to be fitted in the annular recessed part 14 of the body 10, thereby the plunger cap, the body 10 and a plunger can be tightly stuck to each other and retained. At this time, the opening angle θ1 of the retaining claw 8 is set to a range of from 35 to 60 degrees, and an angle θ2 between the adjoining retaining claws 8, 8 is set to a range of from 60 to 85 degrees, and also the height of the retaining claw 8 is set to 0.15 to 0.35mm. Hereby, a lip part 18 except for the retaining claw 8 is deformed only within an elastic range and a crack may not occur, and also a part of external force used for deformation becomes elastic tightening force, thus the plunger and the body 10 can be sufficiently tightly stuck to each other and retained.