A heated ultrasonic treating device (6) comprising a sump (13) through which suspended matter-containing liquid passes, a temperature-controllable heater (14) disposes in the sump (13), and a ultrasonic vibrator (15) disposed in the sump (13). The heated ultrasonic treating device (6) uses the ultrasonic vibrator (15) to apply ultrasonic waves while heating organic drain passing the sump (13) with the heater (14), thereby pulverizing suspended matters and reducing the amount of SS. In addition, a treating column, where pulverized suspended matter-containing liquid is aerobically treated by aerobic microorganisms, is prevented from efficiency lowering due to clogging.