Abstract: A first insulation layer (3), a first conductive layer (1), a second insulation layer (4) and a second conductive layer (2) are laminated, and a larger spacial gap between either one (2) of the first conductive layer (1) and the second conductive layer (2) and the opposite layer (3,4) thereto (2) than that between the other conductive layer (1) and the opposite layer (3,4) thereto (1) is made, and high voltage is applied across both conductive layers (1,2), and when charged dusts pass therethrough, the charged dusts are attached on only one (2) of the conductive layer. These charged dusts are electrically neutralized, and thereby, it becomes possible to prevent weakening of the electric field and declination of the dust-collecting ratio through lapse of time.