PURPOSE: To purify the waste water produced from the washing of cars, etc. for the reuse, by setting alternately a desired number of an ionic oil-water separating tanks and coagulating tanks within a low path of the waste water and applying electrically the electron to the waste water for neutralization.

CONSTITUTION: The waste water produced from the washing of cars, etc. is stored in a tank 1 through a pipe 14 and sent to a sand precipitating tank 2 linking the tank 1 at the bottom part for the precipitation of sand. In this case, the floating-up of the floating matters is prevented by an oblique plate. The waste water is then sent into the 1st coagulating tank 3 through the upper edge of the tank 2, and the oil component is coagulated by the filtering function of zeolite. The water is led to the 1st ionic oil-water separating tank 4 linking the tank 1 at the bottom part to receive the oil-water separation through a mutual electrode plate 19 and beased on the ionic neutralization. Then the water is treated by the 2nd coagulating tank 5, the 2nd ionic oil-water separating tank 6 and the 3rd coagulating tank 7 respectively to be sent into a composite purifying tank 8 to receive the oil-water separation by the mutual electrode plate group 8a. or such waste water, the oil component is immediately coagulated and filtered through a coagulating and filtering matter 8b. Thus the waste water is completely purified and stored in a tank 9.