An image forming apparatus includes: a photosensitive body which is moved in a movement direction; an exposing unit which exposes the photosensitive body, and which includes a guide roller configured to contact with the photosensitive body and rotate with a movement of the photosensitive body and configured to regulate a positional relationship with the photosensitive body, the guider roller being disposed such that a rotation direction of the guide roller is inclined with respect to the movement direction so as to generate a force for urging the exposing unit to one end thereof in an orthogonal direction when the guide roller rotates, the orthogonal direction being orthogonal to the movement direction and to an optical axis direction of a light emitted from the exposing unit; and a regulating member configured to contact with the one end of the exposing unit to regulate a position of the exposing unit.