An optical scanning apparatus and an image forming apparatus including the optical scanning apparatus, the optical scanning apparatus includes a dust-proof shutter having an opening portion. The opening portion has a side-surface opening portion and a top-surface opening portion. The side-surface opening portion is formed in a side surface of the dust-proof shutter. A cleaning member used for cleaning a dust-proof glass is inserted through the side-surface opening portion. The top-surface opening portion guides a moving direction of the cleaning member inserted through the side-surface opening portion, to a direction along a longitudinal direction of the dust-proof glass. When the dust-proof shutter is located at a first position, a light beam passed through the dust-proof glass passes through the top-surface opening portion.