An exposure device includes an optical system member that forms an image of light from a light emitting element array having multiple light emitting elements arranged, an optical system support part that supports the optical system member, and a restraining member that restrains the optical system member to the optical system support part. The optical system support part has sliding parts, which are able to slide relative to the restraining member, formed on a light emitting element side face and an image forming side face in positions opposing the both end parts or the vicinity of both end parts in a longitudinal direction of the optical system support part, and in the both end parts or in the vicinity of the both end parts in the longitudinal direction, the restraining member is formed between the sliding parts and the optical system member, fixed to the optical system member, and slidable in the longitudinal direction relative to the optical system support part.