This invention aims at enhancing the productivity and quality of products in the production line of the automobile seat manufacturing factory, in which, in a device for bonding and molding sheet semi-finished products (3) each consisting of an inner material (4) and outer one (5) between which thermosoftening bond is interposed by heating and cooling said products in the mold, this mold is composed of a hollow half (1) and pressing half (2); the surface of the hollow half (1) in contact with the sheet semi-finished product (3) is perforated; steam piping (14) provided with a steam valve (17), compressed air piping (15) with an air valve (18), and exhaust piping (16) with an exhaust valve (19) are connected to the inner space (8) of the hollow half (1) of the mold; and control means for controlling the temperature in the inner space (8) of the hollow half (1) to a preset one and another means for controlling the opening/closing operation of said valves (17, 18, and 19) are provided.