An optical sensor, comprising: a light emission system configured to emit an irradiated light of a linear polarization in a first polarization direction toward a surface of a target object from an incident direction which is inclined with respect to a normal direction of the surface; a first light detection system comprising a first light detector and a polarizing filter arranged on a first light path of a diffuse reflected light which is diffusely reflected from an incident plane on the target object, the first light detector receiving first light passed through the polarizing filter, the polarizing filter being configured to pass a linear polarization component of a second polarization direction perpendicular to the first polarization direction; a second light detection system comprising a second light detector, without a polarizing filter, arranged on a second light path of the diffuse reflected light which is diffusely reflected from the target object on the incident plane on the target object; and a third light detection system comprising a third light detector arranged on a third light path of a specular reflected light, which is emitted from the light emission system and is specularly reflected from the target object; wherein the first light detection system and the second light detection system are provided for detecting diffused light different from each other in polarization, and arranged on different light paths, which are each different from a light path of specular reflected light which is emitted from the light emission system and is specularly reflected from the target object. a light emission system configured to emit an irradiated light of a linear polarization in a first polarization direction toward a surface of a target object from an incident direction which is inclined with respect to a normal direction of the surface; a first light detection system comprising a first light detector and a polarizing filter arranged on a first light path of a diffuse reflected light which is diffusely reflected from an incident plane on the target object, the first light detector receiving first light passed through the polarizing filter, the polarizing filter being configured to pass a linear polarization component of a second polarization direction perpendicular to the first polarization direction; a second light detection system comprising a second light detector, without a polarizing filter, arranged on a second light path of the diffuse reflected light which is diffusely reflected from the target object on the incident plane on the target object; and a third light detection system comprising a third light detector arranged on a third light path of a specular reflected light, which is emitted from the light emission system and is specularly reflected from the target object; wherein the first light detection system and the second light detection system are provided for detecting diffused light different from each other in polarization, and arranged on different light paths, which are each different from a light path of specular reflected light which is emitted from the light emission system and is specularly reflected from the target object.