Patent ID: 7751042

Claim:
A recursive-reflective photoelectric sensor comprising: a sensor main body including a light projecting part that projects first circularly polarized light and a light receiving part that selectively receives, when a mixture of the first circularly polarized light and second circularly polarized light which is differently polarized from said first circularly polarized light is incident thereto, said second circularly polarized light; and a recursive reflecting part that reflects said first circularly polarized light by converting into reflected light that includes said second circularly polarized light; wherein said sensor main body includes: a light projecting element; a light receiving element; a first phase-shift plate that converts first linearly polarized light into said first circularly polarized light and said second circularly polarized light into said first linearly polarized light; and a first polarization filter that is placed between said light receiving element and said first phase-shift plate on a optical path from said recursive reflecting part to said light receiving element and serves to selectively allow said first linearly polarized light to pass therethrough.