A method for controlling an optical scanning apparatus, includes generating an exposing signal from a pattern data for an optical scanning apparatus, which includes a light source that emits a light beam, a deflector that deflects the light beam emitted from the light source by means of a deflection mirror surface oscillating sinusoidally, and a scanning optical system that has an arcsine characteristics and that images the light beam deflected by the deflector on a surface-to-be-scanned in a spot, and which makes the imaged spot scan the surface-to-be-scanned in the main scanning direction while modulating the light beam emitted from the light source based upon the pattern data indicating a position on the surface-to-be-scanned the light beam exposes so that the light beam exposes a predetermined position on the surface-to-be-scanned, the exposing signal being a train of pulses arranged on a time axis in accordance with an arrangement in the main scanning direction of values, which the pattern data have, indicating exposure or non-exposure of the light beam, a pulse width of each pulse of the pulses being width of time corresponding to a length, indicated by the pattern data, in the main scanning direction of an exposing area of the light beam; correcting the exposing signal to generate a corrected exposing signal by varying pulse width of each pulse of the pulses which compose the exposing signal in accordance with a distance between the exposing area corresponding to the pulse and an optical axis of the scanning optical system; and emitting the light beam from the light the light beam is/are varied in accordance with a distance between the exposing area and an optical axis of the scanning optical system.