A recursive-reflective photoelectric sensor has a sensor main body and a
recursive reflecting part. The sensor main body includes a light
projecting part that projects first circularly polarized light and a
light receiving part. When a mixture of the first circularly polarized
light and second circularly polarized light which is differently
polarized from the first circularly polarized light is incident to the
light receiving part, only the second circularly polarized light is
selectively passed. The recursive reflecting part reflects the first
circularly polarized light by converting into reflected light that
includes the second circularly polarized light.