PURPOSE: To eliminate deterioration of process liquid which is the emulsion of water and oil and also reduction of processibility by providing a process liquid regenerator in a process liquid circulater.

CONSTITUTION: The construction comprises a processing tank 12 in which the discharge processing is carried out in the process liquid 10 which is the emulsion of water and oil and a process liquid circulating device 16 which circulates the liquid 10 in the tank 12 while maintaining a constant resistivity with a process liquid regenerator 16. Liquid 10 in an exhaust tank 22 is forced out by a pressurizing pump 26 to a supply tank 24 through a filter 28 which uses paper, cloth, etc. Waste of the process liquid 12 is eliminated, since the regenerator 14 is provided in the circulator 16. The process liquid 10 may be the emulsion of water and oil. The discharge processing capacity is never reduced due to deterioration of the process liquid 10 so that the productivity can be greatly improved.