PURPOSE:To effectively storage the latent heat by a method wherein the recovering unit of the bottom of a heat storage tank is provided with an inclined surface, on which liquid, heavier than water, is collected, and a preventing means of generation of vortex is provided in a latent heat storage device, in which cold heat is stored by producing sherbet type ice in a heat storage layer utilizing night electric power and the like. CONSTITUTION:In a district heat supplying plant installed in the underground floor of a tall building, an ice heat storage water tank 10 is provided so as to be neighbored to a plurality of water tank units, formed by dividing an underground chamber 1a by partitioning plates 11, while inclined surfaces, slanted downward toward the central part from the periphery thereof, are formed on the bottom of the tank 10. Water is used as a first liquid W or a latent heat storage medium and unsoluble liquid Wa, which will never be mixed with each other and having a solidifying point lower than the same of the first liquid, is used as a second liquid while the recessed part at the central part of the bottom of the heat storage water tank 10 is formed as the stagnating unit 10a of the second liquid Wa. A vortex generation preventing unit 10b consisting of porous plates is provided above the stagnating unit 10a and the suction side of a refrigerating machine 18 is connected to the stagnating unit 10a through a supplying tube 19.