PURPOSE: To provide a light beam scanning optical system by which excellent constitution can be taken in respect of realization of high performance, realization of a high view angle, downsizing, an environmental variation resistant characteristic, a price or the like.

CONSTITUTION: In a light beam scanning optical system arranged between a deflecting means to deflect a light beam and a surface to be scanned, the optical system is composed of two lenses of a first lens 6 composed of a cylindrical lens 4 having positive power only on a main scanning cross section or an a toric lens which has positive power on a main scanning cross section and whose sub-scanning cross section has only power close to zero and a second lens 7 which is arranged in the vicinity of a surface side to be scanned of the first lens 6 and which is composed of a toric lens whose both main and sub- scanning cross sections have positive power, and is characterized in that at least a single surface of the main scanning cross section of the first lens 6 is turned into an aspheric surface, and that at least a single surface of the main scanning cross section of the second lens 7 is turned into an aspheric surface.