PURPOSE: To decrease the unevenness of illumination, to obtain excellent input picture, and to miniaturize a device size by making light from a light source incident on a surface corresponding to the cross section of an optical prism.

CONSTITUTION: For example, a fingerprint is abutted on a surface acdf to be the bottom surface of an optical prism 21, and the light from a light source 22 is made incident on a surface abc corresponding to the cross section of the optical prism 21. At such a time, a fingerprint picture projected on a surface bcef of the optical prism 21 is image-picked-up by a television camera 23. The light falling on the recess part of the surface of a finger out of the incident light from the light source 22 to the optical prism 21 does not arrive at the image pickup surface of the television camera 23, and only the light falling on the projecting part of the surface of the finger arrives at the image pickup surface of the television camera 23. Thus the unevenness of the illumination is eliminated, the excellent input picture can be obtained, and the device size can be miniaturized.