PURPOSE: To improve the service life of a filter, and set it reusable by selecting ability of a supply pump or the like in such a way that dielectric is sent to a filtration column, in which a particulate filter medium to form a labyrinth filtration part is loosely filled, at a speed of at least 2m/min.

CONSTITUTION: A labyrinth filter for spherical particulates is provided with two filtration columns A, B in which particulate filter medium K is loosely filled in a housing 36, a supply pump FP is disposed at inlets EA, EB, and a flow speed of dielectric passing the filter medium K is selected to be at least 2 m/min., favorably 3 m/min. A backwash pump RP for backwash is connected to an outlet connection parts AA, AB, and backwash is conducted while providing free motion to the filter K. A service life of the filter for micro-spherical metal grain generated from an electric discharge machine can thus be elongated, it can be easily cleaned to be reused, and it can be full-automatically operated for a long time.