PURPOSE: To prepare a comfortable seat cushion body without harming the external appearance of the cushion body by providing small dents at necessary places of a foam molded body and projections inside each of these dents.

CONSTITUTION: A foaming mold 5 is composed of a top and a bottom force 6, 7 and a bowllike convex mold part 9 to mold a dent 3 that swells from mold surface 8 for molding a seat surface 2 is provided at the necessary places of the top force 6 and besides, the air vent 12 connectig with the inside space part 11 penetrates the wall 10 of this convex mold part 9. Cushion body foaming stock solution is injected into this mold 5 and a cushion body 1a provided with the dent 3 on the specified place of the surface (on the seat surface 2 or the position corresponding to the convex part 9) is expanded and matured and at the same time the surplus of the cushion body foaming stock solution is made to flow from the air vent 12 into the space part 11 and expanded to make the projection 4 inside the dent 3.