In an exposure device, a beam emitted from a light emitting point of a laser diode (LD) is limited by a slit. The slit limits a light beam in a direction orthogonal to an active layer of the LD. The exposure device has a moving mechanism which moves a plate in which the slit is provided, in a direction orthogonal to the plate. Object points are different at a beam and at flare light. Therefore, the plate is provided in a vicinity of the light emitting point in order to limit the light beam in the vicinity of the light emitting point, i.e., at a place near a point where a beam spot is smallest, and to be able to effectively block only the flare light.