There is disclosed an optical scanning apparatus for effecting the scanning with plural light beams, without aberrations among the obtained scanning lines and without curvature in the scanning lines. For this purpose plural light beams emitted from plural light sources are deflected by a single deflector, composed for example of a rotary polygon mirror (27), and guided to respective scanned planes through a scanning condenser lens system (28,29,30a,30b), having the f-ϑ characteristics in the scanning direction and also having plural optical axes in the sub scanning direction.