Using a new molded foaming apparatus wherein chambers 13 and 14, independent from a cavity 4, are formed at the rear sides of a set of dies 2 and 3 for molding a molded foam product, so as to supply such utility fluid as air and steam to the cavity 4 through first openings 30 independently from the chambers 13 and 14, various problems created when forming vent holes are fundamentally solved, and at the same time dispersion of filling density to be caused by not forming vent holes is prevented by supplying the material beads to the cavity 4 while maintaining the pressure in the cavity 4 at a predetermined minus pressure with respect to the pressure in the material tank using the first openings 30. |