PURPOSE: To obviate such a failure as a sterilizes liquid is contaminated in a piping route by supplying high temperature water into the piping route for guiding a liquid fed from a sterilizing device provided additionally in a bathtub and a pool, etc., and allowing the piping route to be subjected to sterilization treatment.

CONSTITUTION: In the device for executing a treatment so that a liquid in a storage tank 3 of a bathtub, etc., is sterilized and held cleanly, this device is provided with a sterilizing device 8 provided with a means for radiating ultraviolet rays, etc., for sterilizing the liquid drawn out of a going piping route 5 by operating a pump 7, and the liquid for passing therethrough is sterilized. the sterilized liquid passes through a branching part 2 and a returning piping route 9 and is subjected to reflux to the storage tank 3. Also, in the case bacteria, etc., propagate on the inside, etc., of the returning piping route 9, and what is called a slime, etc., adhere thereto, valve 14 is opened, and high temperature water heated through a heat exchanger 13 by burner 12 is led into the branching part 2 by a warm water piping route 11, and allowed to flow through the returning piping route 9, by which a treatment is executed so as to sterilize the inside of the returning piping route 9.