An image forming apparatus includes a rotatable photosensitive drum together with first and second chips which include plural light emission elements arranged along a rotational axis of the photosensitive drum so as to expose the photosensitive drum to light emitted therefrom for each of one line extending along the rotational axis. Parts of the first and second chips overlap in a direction perpendicular to the rotational axis. A controller controls actuation of said light emitting elements on the basis of image data, wherein for the overlapped parts, the light emission pattern is controlled to be different for every predetermined number of the lines.