PURPOSE: To excellently hold image quality for a long time by providing a supporting mechanism which supports a casing so that it can rotate with a charging wire as center and a driving mechanism which drives to rotate the supported casing.

CONSTITUTION: Cylindrical shafts 35, 35 are protrusively formed at both ends in the axial direction of the casing 29 and rotatably supported by bearings 37 and 37 functioning as the supporting mechanism provided to a device main body 3. A gear 39 is coaxially fixed to one end in the axial direction of the casing 29 and linked with the driving shaft of a servomotor 43 functioning as the driving mechanism through an idle gear 41. Therefore, the casing 29 which drives the servomotor 43 rotates with the charging wire 31 as center and a position opposed to an aperture 33 is allowed to move with the rotation of the casing 29. Thus, the secular image quality is excellently held.