In an optical scanning apparatus, a light source includes a plurality of light emitting elements. A light beam output from the source is scanned and deflected by a polygon mirror so as to form an electrostatic latent image on a surface of a light sensitive member. A control unit controls the source so that the source outputs the light beam in a first period before a second period in which the light beam deflected by the mirror forms the image. During the first period for outputting the light beam from the source a period for scanning a non-image region of the member in a state in which the rotation speed of the mirror is being accelerated or decelerated is made longer than a period for scanning the non-image region of the member in a state in which the rotation speed of the mirror is controlled at a constant speed.