According to this invention, there is provided a molding method and apparatus which increase the gas permeation speed in obtaining a foamed resin molded product by letting a gas permeate a molten resin material. To achieve this object, a chip- or pellet-like resin material is evacuated and subjected to dehumidifying/drying processing, and replacement processing in an inert gas in a pre-processing unit, the resin material is then held in an inert gas of a predetermined temperature and pressure in an inert gas permeation unit for a predetermined period of time, the temperature and pressure are decreased, the material is fed to a material hopper whose temperature and pressure are controlled, the material is fed to a plasticizing unit to which a gas of a predetermined temperature and pressure is fed, the resin material is melted in the plasticizing unit, the resin material is injected/charged into a mold which is evacuated in advance to a pressure not more than atmospheric pressure, the pressure is restored to atmospheric pressure after the resin material is cooled for a predetermined period of time, and a foamed product is extracted by opening the mold.