A light scanning device includes: a light source; an aperture stop regulating a width of a light beam emitted from the light source; a deflector deflecting and scanning the light beam emitted from the light source; at least one scanning lens forming an image on a scanned surface with the light beam deflected and scanned; and a phase-type optical element. In the light scanning device, a phase modulation portion is provided to at least a portion of the phase-type optical element, and a phase difference between the phase modulation portion and a region other than the phase modulation portion is not π [radian]. Thus, asymmetry in a curve representing the relationship between a beam spot diameter and defocus can be corrected to reduce variation of the beam spot diameter with respect to the defocus. Consequently, highly-accurate light scanning can be performed.