A foaming molten resin (R) containing reinforcement fibers and super critical fluid is injected into a cavity (23) with a short shot, the foaming molten resin (R) is made self-foam and flow in the cavity (23), and a volume of the cavity (23) is increased by expanding molds (21,23) so as to expand the foaming molten resin (R) in the cavity (23). During the expansion step, the expansion of the foaming molten resin (R) is assisted by gas vent, vacuum suction, partial pressure adding with gas or resin, or a spring back force of the reinforcement fiber in the foaming molten resin (R). Accordingly, there can be provided a resin foam molded article that has no improperly large air voids therein, a sufficient volume expansion thereof, and a superior transferability function.