A heat storage device comprising: two or more reactors including a first reactor having a heat storage material containing a physical adsorbent that stores heat when water vapor is desorbed and radiates heat when the water vapor is immobilized by physical adsorption, and a second reactor having a heat storage material containing a chemical heat storage material that stores heat when water vapor is desorbed and radiates heat when the water vapor is immobilized by a chemical reaction; and a water vapor pipe connecting the two or more reactors to cause the water vapor to flow between the two or more reactors , characterized in that the water vapor pipe includes at least one of a pressure control means configured to control the difference in the water vapor pressure between the two or more reactors , such that when heat is applied to one of the two or more reactors , the pressure control means can be operated to raise the water vapor pressure at a side of the reactor to which the heat is applied so that the reaction rate of immobilization at the other of the two or more reactors can be made faster, or to raise the water vapor pressure at a side of the other of the two or more reactors so that the reaction rate of immobilization at the other of the two or more reactors can be slowed down, and a volume control means that includes a cylinder and a piston and configured to control a volume of the water vapor pipe by moving the piston inside the cylinder such that a volume inside the cylinder is increased or decreased, wherein the water vapor desorbed from one of the reactors is immobilized in the other reactor by using a difference in water vapor pressure between the two or more reactors . two or more reactors including a first reactor having a heat storage material containing a physical adsorbent that stores heat when water vapor is desorbed and radiates heat when the water vapor is immobilized by physical adsorption, and a second reactor having a heat storage material containing a chemical heat storage material that stores heat when water vapor is desorbed and radiates heat when the water vapor is immobilized by a chemical reaction; and a water vapor pipe connecting the two or more reactors to cause the water vapor to flow between the two or more reactors , characterized in that the water vapor pipe includes at least one of a pressure control means configured to control the difference in the water vapor pressure between the two or more reactors , such that when heat is applied to one of the two or more reactors , the pressure control means can be operated to raise the water vapor pressure at a side of the reactor to which the heat is applied so that the reaction rate of immobilization at the other of the two or more reactors can be made faster, or to raise the water vapor pressure at a side of the other of the two or more reactors so that the reaction rate of immobilization at the other of the two or more reactors can be slowed down, and a volume control means that includes a cylinder and a piston and configured to control a volume of the water vapor pipe by moving the piston inside the cylinder such that a volume inside the cylinder is increased or decreased, wherein the water vapor desorbed from one of the reactors is immobilized in the other reactor by using a difference in water vapor pressure between the two or more reactors . <EOS>