An image forming apparatus capable of preventing the image formation unit from being attached to a guide member for the image formation unit mistakenly, including an apparatus body; an image carrier including a rotary shaft; an exposure device configured to form a latent image through exposure of a surface of the image carrier and retractable from an exposure position; an image formation unit disposed detachably from the apparatus body; and a guide member to guide the exposure device to the exposure position. In the optimal apparatus, the guide member is used both to guide the image formation unit to the apparatus body and to guide the exposure device to the exposure position.