Abstract: A fusing device for an electrophotographic image forming apparatus. The fusing device includes a heat pipe, both ends of which are sealed and in which a predetermined amount of a working fluid is contained, a cylindrical roller which surrounds the heat pipe, and a heating element which is installed between the cylindrical roller and the heat pipe. The working fluid is supercooled at room temperature, and crystallizing and producing heat when acted on by a mechanical force, and at least one mechanical unit applies a mechanical force to the heat pipe and crystallizes the supercooled working fluid.