PURPOSE: To obtain a change-over apparatus simple to operate, by introducing left and right branch pipes into a suction pipe into which the hot water of a bathtub is introduced and providing a diaphragm equipped with a return means at the center between the openings of the branch pipes and respectively connecting the left and right branch pipes and a specific branch pipe to bypasses respectively provided with opening and closing solenoid valves.

CONSTITUTION: When the first and second opening and closing solenoid valves 9a, 9b are opened, a diaphragm 6 receives the almost equal pressures of hot water at both surfaces thereof to be returned to a neutral position by a return means 7 and hot water containing air bubbles is injected and returned to a bathtub 1 in equal parts from branch pipes 2a, 2b. When the second opening and closing solenoid valve 9b is opened by operating an operating button, the hot water is returned to the branch pipe 2b through the second bypass 10b and the pressure on a side where a flow rate increases by the return quantity of hot water lowers. Whereupon, the diaphragm 6 on the pressure lowered side performs deflecting operation to close an opening 5a on this side and the hot water is injected and returned to the bathtub 1 only from the branch pipe 2b. Next, when the operating button is operated to open the first opening and closing solenoid valve 9a, an opening 5b is closed in the same way and the hot water is injected and returned to the bathtub 1 only from the branch pipe 2a.