PURPOSE: To rationalize shaping of a product, by making square both the surrounding wall of the heating steam chamber at the cross section vertical to the moving direction of the mold and the shape of the female mold in the molding apparatus provided with the heating steam chamber having a movable back wall.

CONSTITUTION: It is constituted so as the volume of a heating steam chamber 4 can be adjustable correspondingly to the size of a mold by making the length of surrounding wall 8 of the heating steam chamber 4 which encloses a female mold 2 from its outside enough long in the direction of the mold movement and also by making the back wall 7 of the heating steam chamber 4 to approach and retire to and from the bottom wall 6 of the female mold 2. Further, both the surrounding wall 8 of the heating steam chamber at the cross section rectangular to the moving direction of the mold and the shape of the female mold 2 are made square. By this, an areally economical result concerning shaping of the product is made to obtain and also saving of energy is intended by rationalizing consumption of heating steam and cooling water etc.