Provided is a heat storage device (10) of the present disclosure comprises a heat storage material (12) containing sodium acetate trihydrate; a first electrode having a surface which is in contact with the heat storage material and formed of at least one selected from the group consisting of silver, a silver alloy, and a silver compound; a second electrode in contact with the heat storage material; an inorganic porous material contained in the heat storage material; and a power supply (14) for applying a voltage to the first electrode and the second electrode. The inorganic porous material has an average pore diameter of not more than 50 nanometers. The present invention provides a heat storage device capable of releasing heat by releasing a supercooled state by voltage application. The heat storage device can be used repeatedly.