PURPOSE: To make the attenuation of the quantity of the charge small and to increase the collecting efficiency of dust by laminating a negative charge net and a positive charge net whose surface material is located on the plus side of the negative charge net in the electrification rank alternatively so that they may come into contact with each other.

CONSTITUTION: A negative charge net which is electrified at negative polarity and a positive charge net which is electrified at positive polarity and whose surface material is located on the plus side of the negative charge net in the electrification rank are laminated alternately so that the nets may come into contact with each other. For example, a filter consists of three nets where on both the sides of a net electrified at one polarity (inner layer net) 1, nets electrified at the other polarity (outer layer nets) 2, 3 are put and the nets are integrated into one body by a frame body 4. A silicone resin, etc., are preferably used as the positive charge net, and on the other hand, a fluororesin, etc., are preferably used as the negative charge net. In this way, the attenuation of the quantity of the charge is small even when the net is used in an atmosphere of high humidity or washed with water. Therefore, the collecting efficiency of dust is high and stable, and the net has an advantage over nonwoven fabric in air flow resistance and scattering of fiber.