To control and correct the flow rate of inflow water to be treated into an ozone contact pond by measuring the gas pressure (Δp) inside a waste ozone line.

This method comprises: measuring the gas pressure 13 inside a waste ozone sample line; receiving the actual measured value of the gas pressure 13 in a pressure-correcting calculation section 14; and applying correction for the flow rate control of lifted water to a lift pump suction wall water level or to a flow rate controlling calculation section 11 both functioning as a control system of a lift pump 2, by the pressure-correcting calculation section 14, accordingly to the gas pressure 13 inside the waste ozone sample line. Thus, by measuring the gas pressure 13 (Δp) inside the waste ozone line and controlling the inflow water to be treated into an ozone contact pond, the operation control of an advanced treatment equipment can stably and safely be performed.