When manufacturing a disk valve having a ring-shaped elastic seal member fixed to one side thereof for use in a cylinder type hydraulic shock absorber, a disk valve blanked from a plate material is set on a bottom of a lower mold member that is curved to be convex on one side. Mold clamping is performed to form a cavity by a cylindrical mold part and to press the disk valve with a press part to deform the disk valve into a shape that is convex on one side. In this state, the cavity is filled with a rubber material through a passage and vulcanized and cured to mold and fix an elastic seal member to the disk valve. At this time, the disk valve is deformed in a direction in which the curvature reduces by shrinkage of the rubber material.