PURPOSE: To make it possible to supply the coldness in a heat accumulating tank to the other end of a heat pipe without using power by providing a heat pipe one end of which is connected to a heat accumulating tank, ice making section and the side section of the heat accumulating tank and transfers coldness due to the melting heat of ice which is made in an ice making section.

CONSTITUTION: Ice is made in a heat accumulating tank by the electric power during midnight which is inexpensive. In other words a high pressure coolant which has been compressed by a compressor 22 becomes a liquid as it passes through a condenser 24 and cooled there. The coolant, now a high pressure liquid, passes through an expansion valve 26 in a piping 25 and loses its pressure, then the coolant performs refrigerating action by evaporation at a low temperature in an ice making section. By the refrigerating action performed by an evaporating coolant like this, the water in the heat accumulating tank 10 is turned into ice from near the bottom, making ice in the tank 10. Next, the evaporated coolant goes up in the water in the heat accumulating tank, and reaches the compressor 22 via a piping 21 from the top of the tank 10, and the coolant is compressed by the compressor 22 and liquefied by the condenser 24. Then it is again evaporated in the ice making section 14 to perform refrigeration. It is, therefore, possible to keep the total water temperature at near 0°C in the heat accumulating tank without using any external power.