An image forming apparatus includes a cartridge and a casing. The cartridge includes a photosensitive drum, a developing roller, a developing frame, and a drum frame. The developing frame is movable between a contact position and a separated position. A separating member provided on the drum frame acts on the developing frame, so that a reaction force is exerted in a reaction force direction. The casing includes a positioning member, an urging member, and a separation pressing member. The positioning member has a first surface and a second surface. The urging member is configured to urge an end portion of the photosensitive drum toward the positioning member in an urging direction. The first surface is configured to support the end portion at a position downstream of the urging direction. The second surface is configured to support the end portion at a portion downstream of the reaction force direction.