PURPOSE: To detect irregularities with clear contrast, by providing a transparent body, having a detecting surface to which a sample body is contacted, by utilizing a light beam, which advances in the transparent body at an angle that is greater than a critical angle regarding a light beam from the inside of the transparent body under the state the sample body is not contacted, among the reflected light beams from the sample body having irregularities.

CONSTITUTION: A light beam is incident on an interface (interface α) between prism 1 and air from the side of the air. The light does not advance in the prism 1 at an angle, which is larger than a critical angle at the interface α with respect to a light beam emitted from the inside of the prism 1, even though the light beam is made incident at any angle. Under the free state where a contacting body is not present, the light beam emitted from the inside of the prism 1 is made insident on a detecting surface 3. A fingerprint surface 2 is contacted with the detecting surface 3. The light beams are reflected from the fingerprint surface 3. Of the reflected light beams, the light beam, which advances in the prism 1 at an angle larger than the critical angle at the detecting surface 3 with respect to the light beam from the inside of the prism 2 under the free state, is detected. Thus the irregularities of the fingerprint surface 2 can be clearly detected.