An image forming apparatus includes process units arranged in a predetermined direction to form a process-unit row, each having a photosensitive body and a developer container; a casing accommodating the process units and having a cover opening and closing an opening formed at one side in the predetermined direction, and an exposure member exposing the photosensitive body, and having a laser source, a deflector, and an optical element, and the exposure member is arranged facing the developer container of each process unit in a direction orthogonal to the predetermined direction. The process units are detachable from the casing, through the opening of the casing, and the developer container of one process unit arranged at one end of the process-unit row has a protruding portion protruding toward the exposure member to overlap with the exposure member in the orthogonal direction.