A light-beam scanning apparatus is disclosed in which a mirror surface of a metal having a characteristic that the reflectance of the mirror surface increases as the incident angle of light incident on the mirror surface is larger, is used as a reflecting surface (4), the optical thickness nd of a transparent protective film (5) formed on the reflecting surface is made substantially equal to mλ/2 (where n, d, m, and λ indicate the refractive index ofthe protective film, the thickness of the protective film, an integer, and the wavelength of the incident light, respectively), the incident light is linearly-polarized light, and the direction of vibration of the linearly-polarized light is inclined atan angle of about +45°to -45°to a direction perpendicular to the plane of incidence of the linearly-polarized light.