PURPOSE: To contrive reduction of capacity of quantity of heat and energy saving of a gas burner for hot water supply device, by preheating cold water to be supplied to a heating pipe of a hot water supply device by remaining hot water in a bathtub and controlling a supply quantity of gas to the gas burner for the hot water supply device according to a temperature of hot water within the heating pipe of the hot water supply device.

CONSTITUTION: When a valve 5a is opened, a hot water supply pipe 8 is connected by a cock 9 with either a shower head 10 or a fresh hot water pipe 11 and cold water from a city water pipe 5 is flowed to a heating pipe 7 for hot water supply side through an indirect heating pipe 6, the cold water is heated within the pipe 6 by the remaining hot water in the bathtub 1. Quantity of heat for heating the heating pipe 7 by a burner 16 for hot water supply, therefore, can be reduced. At the time of heating by the burner 16, wax container 29 is pushed leftward of a valve body 31 through a push rod 30 and a thermo control valve 27 is actuated to a closing side according to a water temperature as the wax container 29 is heated by an increased temperature of the water within the heating pipe 7.