An image forming apparatus has: a photosensitive drum as an image holding body to form an electrostatic image; a charging roller which is arranged so as to face the drum and charges it; pressing springs which apply a pressing force to the charging roller toward the drum; and spacer members as gap holding members which are attached to both sides of the charging roller, are come into contact with the drum surface, and hold a gap between the drum and the charging roller. The pressing force of the springs and a frictional coefficient between the drum and the spacer members are set in order to driven-rotate the charging roller to the drum at the same peripheral velocity by a frictional force occurring between the drum and the spacer members. The apparatus uses a contactless charging system for realizing high charging performance, high picture quality, and high durability.