To provide a heat storage device to shorten a separation time of a solid heat storing material to 1/3.

This device is formed such that a heat exchanger 4 is immersed in a liquid heat storage material 2 in a tank 1, and after the liquid heat storage material 2 is crystalized on the surface of a heat-exchanger 4, heat is stored as a crystalized heat storage material is peeled. In this case, a means is provided to exert a volume power on the solid heat storage material 3 crystallized on the heat-exchanger 4 when the solid heat storage material 3 is peeled. By using, for example, an air compressor as the means to exert the volume power, compressed air is injected against the solid heat storage material 3 crystalized on the heat exchanger 4.