To provide a method of manufacturing the plug for an accumulator capable of simplifying the manufacture of the plug, solving the problem of contamination as well.

The method of manufacturing an accumulator plug whereby a vulcanized molding is performed with a poppet 4 being installed in a product cavity 22 in molding a plug body having a rubbery elastic film by the use of a molding die 21, provides a stepped part 25 on the inside wall of the product cavity 22 beforehand at the outer peripheral side of the poppet 4 disposed in a given position of the product cavity 22 and further forms a prescribed gap 26 in the radial direction between the side face 4a of the poppet 4 and the stepped part. The vulcanized molding is thus carried out with a part of molding material 3A being filled in said gap 26.