PURPOSE: To surely distinguish a beam reflected by an objective reflecting body from a beam reflected by a nonobjective reflecting body which is optically similar to the objective body, by dividing the objective reflecting into a polarization converting part and a reflecting part.

CONSTITUTION: An objective reflecting body 2 is composed of a substrate 27 formed thereon with a reflecting layer 28, and a λ/4 birefringent member 29 applied to the reflecting layer 28. The exposed part of the reflecting layer 28 is used as a reflecting part for reflecting an impinging light beam while its polarizing direction is conservative, and the λ/4 birefringent member 29 is used as a polarization converting and reflecting part for reflecting the impinging light beam while its polarizing direction is converted. Meanwhile, an objective reflecting body detecting device illuminates a polarizing illumination light beam from its body part to the objective reflecting body 2, and receives the polarizing and reflecting light beam therefrom. A first detecting means detects the polarizing reflecting beam, and a second detecting means detects a polarizing light beam other than the polarizing and reflecting light beam. A reflecting beam detecting circuit compares the output of the first detecting means with that of the second detecting means so as to distinguish the objective reflecting body 2, thereby it is possible to prevent the objective reflecting body 2 from being erroneously detected.