PURPOSE: To mold the titled foamed object of a large size and a light weight, by pouring a foaming plastic stock liquid in a closed mold and foaming it, reducing the pressure inside the mold.

CONSTITUTION: By putting a rubber packing 3 between the peripheral parts of a bottom force 1 and the top force 2 of a foam molding mold 10 and clamping them by clamping jaws 5 the closed space of a fixed form is shaped between the bottom and top forces 1 and 2. The predetermined amount of a liquid isocyanate component and that of a liquid polyol component are supplied from material supply pipes 8 and 9 respectively, mixed in a mixing head 4 and poured from a stock liquid pouring port 7 into the mold. The pressure in the mold is reduced by a vacuum pump via an air aspirating pipe 6 and when a poured stock liquid begins to foam, the constant pressure is maintained by aspirating an air correspondingly and a foamed object is molded.