A coupling lens arranged on an optical path of an optical beam from a VCSEL, which has a refraction plane and a diffraction plane that respectively change a power according to a temperature change and suppresses a beam-waist position change in a main-scanning direction and a sub-scanning directions on the scanning surface caused by the temperature change, by a wavelength change of the optical beam caused by power changes of the refraction plane and the diffraction plane and the temperature change. A deflecting unit deflects the optical beam that passed through the coupling lens. A scanning optical system condenses a deflected optical beam on the scanning surface.