PURPOSE: To enable hot bath water to be always kept at a desired temperature by a method wherein hot water is automatically fed within a bath tub to a predetermined water level through an automatic water feeding unit, thereafter a forced circulation of the bath hot water is immediately carried out to make an appropriate heating of the bath hot water through a heat exchanging tank of a hot temperature keeping unit.

CONSTITUTION: In a hot water and cold water mixing device 100, hot water and cold water are fed from a hot water piping system 3 and a cold water feeding pipe system 8 to a hot water and cold water mixing valve 117 through check valves 107 and 108. They are electrically driven and controlled. The hot water and cold water mixing valve 117 is adjusted by a controller 118, a mixing ratio of hot water and cold water is made variable, the hot water is mixed up to a predetermined temperature and then the hot water is fed out through a hot water feedingout port 119. When a condition in which a bath hot water fed in the bath tub A reaches a predetermined hot water level L is sensed by a pressure sensor 309, a solenoid valve 201 of an automatic hot water feeding unit 200 is closed through a main controller MC operated through a remote controlling operation of a remote controller RC3 so as to terminate a hot water feeding operation and at the same time a hot water feeder 1 also terminates its operation and simultaneously a circulation pump 303 of a temperature keeping unit 300 is driven and a forced circulation of bath tub hot water within a bath tub A is performed.