To construct a compact bath circulating purifier, which purifies the water in a bathtub while letting the water flow in a bath circulating duct line, and then returns the water into the bathtub again, at low cost, and also to prevent the water in the bathtub from decreasing by being thrown away to the outside as it is, when washing the purifier using the bath.

This purifier provides a washing circulating duct line 34, which goes through a main tank 26 in a filter 18 and consists of a closed circuit for circulating wash water, separately from a bath circulating duct line 12, in such a manner that the washing circulating duct line 34 goes through the upstream and downstream parts of a circulating pump 14 and that of a bath circulating duct line 34. By the circulating pump 14, the wash water is circulated in the washing circulating duct line 34, and a diverter valve means 22 and 36 are provided to divert a circulating stream from the bath circulating duct line 12 to the washing circulating duct line 34, or vice versa.