a method of molding a headrest of automotive seat comprises the following steps . first , a bag shaped flexible outer skin member is prepared , has an elongate slit formed therethrough . a part of a stay member is inserted into the outer skin member through the slit and set relative to the outer skin member . a given biasing force is applied to longitudinal ends of the slit so that the slit is stretched in longitudinally opposed directions and thus caused to take a closed position . then , an injection nozzle of a foamable material feeder is put into the slit by expanding the slit against the biasing force . a foamable material is poured into the outer skin member , and the material feeding is stopped when a given amount of material is fed to the outer skin member . the application of the biasing force to the slit is continued until the material is sufficiently cured .