Abstract: An optical sensor including an irradiation system including an irradiation system including a light source unit having a light source, the irradiation system configured to emit a linearly polarized light of a first polarization direction onto a surface of an object, a polarizing optical element disposed on an optical path of the light that is emitted from the irradiation system and reflected by diffuse reflection from an incident plane of the object and configured to separate a linearly polarized light component of a second polarization direction, a first photodetector configured to receive the linearly polarized light component of the second polarization direction separated by the polarizing optical element, and a housing supporting the irradiation system, the polarizing optical element, and the first photodetector, where the light source unit is fixed to the housing in a light emitting direction of the light source unit via space.