In this optical scanning device, a plurality of scanning optical systems are arranged in a main scanning direction. Each of the scanning optical systems includes a deflecting unit performing an optical scanning by oscillation. Scanning frequencies of the deflecting units are substantially equal to one another. Each of the deflecting units is provided with means for varying the scanning frequency. The scanning frequency of each of the deflecting units is set midway between a maximum value and a minimum value of a resonance frequency intrinsic to the deflecting unit.