An image forming apparatus includes a plurality of image forming portions, each of which has a photosensitive member and a developing device for developing an electrostatic image on the photosensitive member, and an exposure unit disposed beneath the image forming portions for exposing the plurality of photosensitive members. The exposure unit has a frame member that accommodates an optical member. The frame member includes an upper frame portion opposed to the image forming portions. The upper frame portion has a plurality of recessed portions corresponding to the image forming portions respectively.