An image forming apparatus, having a photosensitive drum assembly, an exposure head, and a bearing, is provided. The photosensitive drum assembly includes a photosensitive drum and a flange disposed at an end of the photosensitive drum in an axial direction of an axis of the photosensitive drum. The flange contacts an inner surface of the photosensitive drum. The exposure head includes a plurality of light emitters aligned along the axial direction of the photosensitive drum, a lens array focusing light from the light emitters on the photosensitive drum, and a head frame to support the light emitters and the lens array. The bearing has a first contact face to contact the exposure head to define a distance between the lens array and the photosensitive drum along a direction of an optical axis of the light.