PURPOSE: To feed the liquid stably at all times by producing a plurality of level signals corresponding to a detection signal of the liquid level in a liquid storage facility, then selecting one level signal from said plural level signals in accordance with the external factors concerning to the demand of the liquid and controlling a liquid feeder.

CONSTITUTION: A liquid storage facility 3 is provided with a liquid level detector 3 and level range setters 51, 52...5n having different setting ranges of liquid level for producing predetermined level signals SH1, SHL... in accordance with a detection signal S from said liquid level detector 4. Said level signals are inputted to a selection circuit 21 in an operation control section 20 so that a selection command circuit 22 selects one of said level range setters 51, 52...5n on the basis of the external factor data provided from an external factor output section 10. When a high level signal is fed from the selected level range setter, an operation stop signal SP is outputted from an operation control signal generator 23 to a liquid feeder, while when a low level signal is fed from said setter, an operation start signal ST is outputted.