In an embodiment of the present invention, a pressure application mechanism portion is provided with a pressure-varying link structure arranged so as to be movable in lateral directions along an upper end portion of a device frame, a drive shaft having an eccentric cam for moving the pressure-varying link structure in the lateral directions, a shaft holding structure arranged so as to be rotatable coupled to the pressure-varying link structure, and a coil spring for applying a biasing force to the shaft holding structure in one direction along the upper end portion of the device frame, and a rotational movement is carried out to make a pressure roller approach and move away from a heat roller so as to achieve a relatively low pressure during a color processing mode and a relatively high pressure during a monochrome processing mode.