PURPOSE: To ensure hot water supply without danger and highly effectual circulation by changing a temperature control set value for controlling a 1-heater 2-passage hot water supplier including a hot water supply circuit and a circuit such as a bath (additional burning function and heating function, etc.).

CONSTITUTION: A flow rate sensor 5 is provided on the way to a water supply pipe 4 which is connected with a heater body 1 of a hot water supplier for detecting a water flow, and detected temperature by a temperature sensor 2 provided on the heater body 1 is inputted into a controller 6. A temperature control set value for the heater body 1 is converted to high and low values with a signal from the flow rate sensor 5, and during the operation of a hot water supply circuit A the temperature control set value is controlled to be low, and during the operation only of a circuit 13 the temperature control set value for the heater body 1 is controlled to be high. A heat exchange efficiency is improved and hence danger such as a burn is prevented.