PURPOSE: To prevent stagnation of bath water in a sucking duct of the bath water of a filth collector after discharging the bath water, and to prevent putrefaction of the bath water and breakage of the duct due to freezing of the stagnating bath water, by providing a drain cock to a lowermost part of the sucking duct of the bath water of the filth collector.

CONSTITUTION: A circulating pipe 9 have a circulating pump 2 of bath water 3a in the middle part of the pipe and communicated to a bath tub 8 is provided. A filth collector 10 which sucks the filth on the water surface of the bath tub together with the bath water by the jet effect of the bath water discharged to the bath tub 8 from the circulating pump 9, is provided to the bath tub 8. A drain cock 14 is provided to the lowest part of the sucking duct 11 of the bath water of the filth collector 10. As the result, the bath water is discharged by opening the drain cock 14 in the discharging stage of the bath water. Thus, the problem of stagnation of the bath water in the filth collector is eliminated, so the putrefaction of the stagnating water and the breakage of the filth collector due to freezing of the stagnating water are prevented. Thus, sanitary condition and safety condition of a bath tub are improved.