In an optical scanning apparatus, a light beam emitted from a light source is deflected and scanned by a light deflecting member, and then scanned and imaged with substantial speed uniformity onto a medium to be scanned by a scanning optical element. The apparatus is configured so that, when the angle formed by the light beam that is deflected and scanned and the optical axis of the scanning optical element is , the amount of positional deviation due to deviation from speed uniformity of the light beam on the medium to be scanned is (), the spatial scan density on the medium to be scanned is P, and the maximum of an absolute value of the angle is o, an expression of |d()/d|5.010/Po holds.