PURPOSE: To mold the titled molded object integrally without causing defectives by a method wherein a cavity part corresponding to a blind part into which original foaming liquid cannot flow is filled previously with foam and the original foaming liquid is injected into a mold.

CONSTITUTION: A cavity part between an intermediate mold 3 and an upper mold 4 is filled in advance with foam 8. Next, original foaming liquid is injected into a lower mold 2, and the upper mold 4 is closed centering the intermediate mold 3. The original foaming liquid is expanded homogeneously in a cavity part 5 between both lower mold 2 and intermediate one 3 but cannot flow into a cavity part between both intermidiate mold 3 and upper one 4 which are connected through a jaw part 3a of the intermediate mold 3 because of a large flow resistance. However, this part is filled in advance with foam 8 and the foam 8 is mixed with the original foaming liquid to provide the back part 7 of a blind part 6 of a bag-shaped cushion body 1.