A line beam scanning optical system includes: a plurality of laser light sources disposed so as to be aligned in a direction corresponding to a long side of a line beam; an optical deflector; a first cylindrical lens configured to converge laser light from the plurality of laser light sources, into substantially parallel light in a direction perpendicular to an alignment direction in which the laser light sources are aligned, and to cause the laser light to be incident on a mirror; and a second cylindrical lens configured to condense the laser light from the plurality of laser light sources, in the alignment direction in which the laser light sources are aligned, and to cause the laser light to be incident on the mirror. The plurality of laser light sources are disposed at positions shifted from a focal position on the laser light source side of the second cylindrical lens.