To permit the temperature regulation of hot-water and improve a heat storage density by a method wherein a heat flow controlling heat transfer device is constituted by sealing evaporative liquid therein and the pressure increase of the device is mitigated to control the amount of heat transportation from an evaporator into a condenser.

Heat is stored in a heat storage body 11 while inputting into a heater 12 utilizing midnight electric power and the like. A minute input is inputted into a heater 8 whereby a part of liquid 4, moved from a tank 3, is boiled. On the other hand, heat of condensation, which is released in the condenser 2 of a heat exchanger 13, is transmitted into a heat exchanging pipe 14. Accordingly, water, flowing through an inlet pipe 15, is heated and is discharged out of an outlet pipe 16 as hot-water for hot-water supplying. Water flow is passed through the heat exchanging pipe 14 so that the internal pressure of the heat flow controlling heat transfer device will not be increased excessively. On the other hand, water is passed through the pipe 14 synchronously with or slightly earlier than the input into the heater 8 of the device. Further, the amount of input into the heater 8 is limited to control the amount of heat transportation from an evaporator 1 into the condenser 2.