An image forming apparatus includes a photosensitive drum, a charging roller, a transfer roller, and a toner charging brush, wherein the toner charging brush reciprocates in a longitudinal direction of the photosensitive drum. In the image forming apparatus, when a number of rotations per a unit time of the image bearing member is assumed to be "a" and a number of times of reciprocation per unit time of the toner charging brush is assumed to be "b" assuming that R=b/a, R is set to be in a range of 1/25.ltoreq.R.ltoreq.3. However, R=m/n (m and n are integers of 5 or less) is excluded. Consequently, generation of a periodic attachment pattern appearing on the photosensitive drum is eliminated.