PURPOSE: To supply hot-water with a proper temperature by a method wherein the title supplier is provided with an additionally heated hot-water supplying passage, connecting the forced circulating passage of bathtub water to a heat exchanger, and a mixing passage, joining the hot-water of a hot-water supplying passage having a water amount control valve on the way thereof with water supplied to the heat exchanger while provided with a water conduction control valve controlling the water supplied to the heat exchanger.

CONSTITUTION: When the additional heating switch of an external controller 23 is operated, a pump 17 is rotated by receiving a command from a controller 22 and water in a bathtub is circulated in a forced circulation passage from the bathtub 16 through an additional heating returning pipe 10 bia the pump 17 and an additional heating sending pipe 9. High-temperature water is mixed with the water in the bathtub 16 circulating by the pump 17 in the additional heating sending pipe 9 to reduce the temperature of the high-temperature water and sent it from the hot-water outlet port 18 of the bathtub. Upon using additional heating and hot-water supplying simultaneously, one part of the high-temperature water of the heat exchanger 3 is mixed with water, introduced from a mixing tube 20 and before entering the heat exchanger 3, by a water amount control valve 4 and a water conduction control valve 21 to supply it from a hot-water supplying passage 5 while the balance of the high-temperature water of the heat exchanger 3 is supplied from an additionarily heated hot-water supplying passage 7 into the forced circulation passage.