PURPOSE: To reduce the vibration of sensible image carrier due to driving devices for rotationally driving a contact charging means without making the device high in cost, large in size and heary in weight in particular.

CONSTITUTION: In this driving devices 300, 202... for the contact charging means 201 provided with a driven side gear 304 for rotationally driving the contact charging means 201 in contact with the sensitive image carrier of an image forming device and applying a charge thereto, a driving side gear 303 directly or indirectly engaged with the gear 304 and rotationally driving it and the driving means 300-302 rotationally driving the driving side gear 303, the number of teeth (a) and the number of ribs (b) of the driving side gear 303 are defined as a=c.b, m<c<m+1 (m is a natural number).