An overfilled optical scanning apparatus has an incidence optical system for converging a light beam onto a deflection surface of a light deflector which has a plurality of deflection surfaces, and an imaging optical system for imaging the deflected light beam onto a surface to be scanned. The imaging optical system satisfies a relationship among its focal length in a main scanning direction, the distance in the main scanning section from the rear principal plane position to an imaging point of the converged light beam, angles in the main scanning section formed by the optical axis of the imaging optical system and the principal ray of the light beams incident on the light deflector, the unevenness of distances in the main scanning section from the rotation center of the light deflector, and the number of pixels per inch in the main scanning direction on the surface to be scanned.