PURPOSE: To provide an apparatus for cleaning bath water equipped with a simple sterilizier effecting sterilization completely harmless to human body.

CONSTITUTION: An ultraviolet irradiation device 7 equipped with an ultraviolet lamp 8 emitting Hartley band ultraviolet rays of 200-300nm wavelength is installed downstream from an ozone mixer 6 which supplies ozone into circulating hot water from an ozone generator 19. In this way, the bath water is effectively sterilized by the combination of ozone and ultraviolet rays. Moreover, the ultraviolet rays do not generate ozone and the unreacted ozone in the water is decomposed into harmless oxygen so that the water ejected to a bathtub is entirely free from harmful ozone.