A scanning optical system configured to scan laser light on a scanned surface in a scanning direction, includes a light source emitting the laser light, a converging element converging the emitted laser light in the predetermined scanning direction, a deflector deflecting the converged laser light to scan the laser light on the scanned surface, and a scanning speed controlling element controlling the deflected laser light to be scanned at a constant scanning speed. The scanning optical system is configured to satisfy predetermined conditions.