PURPOSE: To prevent wasteful dissipation of heat generated from a heat generating substance, to effectively utilize the heat and to suitably heat an object to be heated by providing heat reflecting and heat insulating structures in a portable heat generator utilizing the generating substance.

CONSTITUTION: An air-permeable heat insulating layer 4 having an air-permeable heat reflecting layer 3 is provided above an inner surface of a heat generator 1, and an air-permeable heat absorption transfer layer 2 is provided below thereon. The layer 3 reflects infrared rays radiated from the generator 1 upward to direct is downward. The layer 2 transmits infrared ray directed downward to efficiently radiate it downward. The layer 4 shuts OFF heat from the generator upward by means of heat radiation and conduction. When a heat generator unit 7 is set to a heat generating state and brought at the side with the layer 2 into contact with an object to be heated, the heat generated from the generator 1 is prevented from being wastefully dissipated by the layers 3, 4 and transmitted all to the object through the layer 3 by radiation and conduction.