A heat storage device that includes a first heat storage material and a second heat storage material, both of which accumulate heat by heat exchange with a heat afferent medium, and a changeover device that selectively either performs or intercepts heat storage by the second heat storage material. Accordingly, if the absorption of heat by the first heat storage material has decreased, the changeover device changes flow of the second heat storage material so that heat may be extracted from the heat afferent medium by the second heat storage medium. Thus, when the heat afferent medium is a refrigerant, it is possible to supercool the refrigerant thereof. Furthermore, since heat is extracted from the heat afferent medium and is accumulated, accordingly it is possible to anticipate effective utilization thereof.