A light scanning unit including: a housing including optical components disposed on an optical path, wherein an electrostatic latent image is formed by scanning light beams respectively onto a plurality of photosensitive drums, wherein a plurality of slits are formed, in a sub-scan direction, in both side frames of the housing which face each other; and a thermal expansion control unit disposed on both of the side frames and having a lower thermal expansion coefficient than the thermal expansion coefficient of the housing. Since the change of the scan line due to the thermal deformation may be reduced in the light scanning unit, the light scanning unit may be efficiently applied to electrophotographic imaging apparatuses in any orientation. For example, the light scanning unit may be installed in an electrophotographic imaging apparatus so as to be parallel to or perpendicular to the main body of the electrophotographic imaging apparatus.