PURPOSE: To perform an automatic decreasing in water temperature and water level within a bath tub after feeding water in that bath tub by a method wherein a heating calorie for the bath tub water, cooling amount and an amount of drain water are calculated in response to a water temperature and each of set values at a water level setting part so as to control each of supplying amounts in a hot water passage and a cold water passage and a drain volume in a water discharging passage.

CONSTITUTION: When it is desired to decrease a temperature of hot water and to reduce an amount of hot water, a person taking a bath sets to decrease each of water level and water temperature setting parts 16, 17 down to a desired scale, respectively. To a calculation part 20 receiving the operation signals is inputted each of signals of an amount of hot water Vb(l) and a hot water temperature Tb(°C) of the set target values. Each of signals of the present hot water amount Va(l) rather than a detected signal from the water level sensor 6 and the present hot water temperature Ta(°C) rather than a detected signal of a hot water temperature sensor 7 is inputted to the calculation part 20. Additional condition of a heating calorie N=0 is substituted for a calculation equation 1 and then cold water is supplied from a cold water valve 13 in response to a signal outputted by a driving part 21 receiving an instruction from the calculation part 20 based on this result of calculation. Cold water supplying amount R(l) and water draining amount W(l) are calculated through calculation equations 1, 2 with the signal in which a water amount sensor 14 detects a cold water temperature t(°C) and then the calculation part 20 inputs a signal of this solution into a driving part 21.