A compact optical scanning apparatus capable of desirably correcting an f.theta. characteristic, a field curvature, and other aberrations, and an image forming apparatus using the same, which includes an incident optical system (LA) for guiding a beam from a light source (1) to a deflector (4) and an imaging optical system (LB) for guiding the beam to a scanning surface (7), wherein a scanning field angle region where .theta.1<.theta.3 and .theta.2<.theta.3 are satisfied exists within effective scanning field angle region, where in a main scanning cross section and for a scanning field angle .theta.1, .theta.2 represents an angle between a principal ray of beam incident on an optical element included in the imaging optical system and located closest to the scanning surface and an optical axis of the imaging optical system and .theta.3 an angle between a principal ray of a beam from the optical element and the optical axis.