To dispense with the removal work of a deposit in a tank.

Stirring blades 2 are provided in a tank (e.g. the coolant tank of the cutting liquid circulating supply equipment of a machine tool) T replenished with a liquid C along with solid impurities D or a tank (e.g. the water receiving tank of the water supply equipment of multiple dwelling houses or the like or a fryer tank of a fried food machine) T replenished with the liquid C and generating solid impurities D during the storage of the liquid C. The solid impurities D are equally dispersed in the liquid C without being sedimented by always operating the stirring blades 2 and filtered and removed gradually and slowly by a filter F during the feed-out of the liquid C to the outside of the tank T.