To provide an inexpensive purifying tank provided with a defoaming device certainly enabling defoaming.

In an anaerobic filter bed contact aeration type purifying tank 10 wherein a sludge transfer device 1 is provided above a contact aeration tank 11 and the sewage in the contact aeration tank 11 is pumped up through a pumping-up pipe 3 and adjusted to be distributed to transfer water returned to the first chamber of an anaerobic filter bed tank or the first chamber of a sedimentation and separation tank by the sludge transfer device 1 through a transfer pipe 6 and excessive water returned to the contact aeration tank 11, a water sprinkling means communicating with the sludge transfer device is arranged above the contact aeration tank 11 and excessive water is sprinkled over the upper surface of the contact aeration tank 1 by the water sprinkling means.