PURPOSE: To set a first mold and a second mold at the given temperature and without complicated temperature control and manufacture a product of superior quality by preheating and cooling the first mold on which a skin material is disposed and the second mold to which molten foamed resin is fed directly and respectively by a fluid of constant flow rate and the constant temperature.

CONSTITUTION: A fluid of constant flow rate and constant temperature is fed respectively into a first mold 12 and a second mold 14 and the preheating temperature of the first mold 12 is set lower than the preheating temperature of the second mold 14. Then, a skin material S is disposed on the first mold 12 and molten foamed resin is filled into a cavity 16 formed with the first mold 12 and the second mold 14 and foamed therein by a feeding means 22. After that, the foamed resin is cured in the cavity 16 under the cooling action of the fluid fed into the first mold 12 and the second mold 14 and the skin material S is incorporated integrally therein to manufacture a molded product.