To eliminate a gap between a heater and a member to be tightened and to prevent the local overheating of the heater by constituting the member to be tightened provided inside a counterbore part formed on the respective pressurizing surface side of a fixing plate and a movable plate by fitting a locking part projectingly provided on a resin member to the locking hole of a metallic member provided with a screw part.

The fixed plate 15 provided with a planar heater 14 on the pressurizing surface side is formed by laminated wood or a particle board or the like and the movable plate 17 provided with a cushion body 16 on the pressurizing surface side is also made of the similar wood and is freely turnably connected to one end of the fixed plate 16 by a hinge device 18. At the time, the member 19 to be tightened is arranged inside the counterbore part 20 recessed and provided on the pressurizing surface side of the fixed plate 15 and the movable plate 17 and plural tightening members 22a and 22b for constituting the hinge device 18 are attached by screws 21a and 21b. Then, the respective members 19 to be tightened are integrally constituted by inserting the locking part to the locking hole from the resin member 23 constituted of the electric insulation body of polypropylene resin or the like on the side of the heater 14 and the metallic member 24 provided with the screw part.