PURPOSE: To provide an ice heat accumulating tank capable of increasing a rate of occupying of ice within the tank at a short period of ice making operation.

CONSTITUTION: A heat exchanger 11 operated to absorb heat or radiate heat by circulating thermal medium in a reversible manner is arranged within a tank, ice is formed at the surface of the heat exchanger 11 while being contacted with the heat exchanger 11 and then the ice making plates (8 to 10) for use in peeling off or floating the ice are arranged to form an ice heat accumulating tank 1. Then, the ice making plates (8 to 10) of which shapes are analogus to the shape of the bottom surface are installed at the bottom surface 2 within the tank formed into a rectangular shape as viewed in its top plan view. A plurality of ice making plates (8 to 10) having the same shape as that of the ice making plates (8 to 10) arranged at the bottom surface 2 within the tank are arranged at the wall surface at the lower part within the tank.