PURPOSE: To contrive to improve the efficiency of dust, collection, by charging DC voltage between a couple of metallic collector plates.

CONSTITUTION: A couple of metallic collector plates 3, 3' are provided with a distance apart from each other inside an insulating vessel 1 for circulating water through it, and fine particles contained in the water are let adhere to the collector plates 3, 3' and collected by charging DC voltage between said coupled collector plates 3 and 3'. Thus, the fine particles in the water can be certainly collected on the surfaces of the collector plates 3, 3' at the side of negative potential by circulating the water through the filter. Even when the filter is attached to the part inbetween a water pipe, a head loss caused by the attachment can be suppressed at a very small value.