| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical sensor which identifies a recording medium with high accuracy.SOLUTION: An optical sensor includes: a photodetector 130 which irradiates a recording medium with light from a light source 110, to detect intensity of regular reflection light thereof; and a processing unit 150 which calculates smoothness of the recording medium on the basis of the detected intensity of the light. An aperture plate 170 is provided so that an angle &thetas;11 of an optical axis obtained by connecting an irradiation center to the normal of the recording medium is 70-88°, and an angle &thetas;12 of an optical axis obtained by connecting the irradiation center and the photodetector with respect to the normal is equal to the angle &thetas;11. When a divergence angle smaller than the angle &thetas;12 is &thetas;x1, a divergence angle larger than the &thetas;12 is &thetas;x2, and an angle of light incident on the photoreceptor, out of the reflection light reflected in the irradiation area, is &thetas;, |&thetas;x1|>|&thetas;x2| and &thetas;x1+&thetas;11<&thetas;<&thetas;x2+&thetas;11 are satisfied. |
