PURPOSE: To obtain a slurry pressure-feed device for solid-liquid separation which is simple in its structure with less troubles and has a high reliability, by operating a control device for a diaphragm pump by means of a liquid level switch in a supply chamber within a working liquid tank.

CONSTITUTION: A diaphragm pump 7 pressure-feeds slurry 2 from a slurry tank 1. The diaphragm pump 7 is fed with working oil from a pump 11 through a selector valve 10. The working oil is reserved in a working oil tank 8 which is divided into a return chamber 22 and a supply chamber 21 by an overflow dam 23. Further, the supply chamber 21 is fed with oil which is overflown from the return chamber 22. By means of two switches 28, 29 for detecting the level of liquid in the supply chamber 21, the selector valve 10 and the pump 11 are controlled.