To surely detect the lines of a knuckle with a relatively small number of pixels by providing a sensor surface where pixels in which the length of a direction orthogonally crossing the longitudinal direction of the finger is made longer than the length of the longitudinal direction are arranged two-dimensionally.

When a joint part on the side of the palm of the hand of, e.g. a finger 15 is placed on one plane 12a constituting the right angle of a prism 12, light from a light source 11 is made incident on a diagonal plane 12c of the prism 12 to illuminate the line surface of the joint part of the finger 15. Reflected light from the line surface is reflected against the plane 12c of the prism 12 and is received by a two-dimensional sensor 14 through an image forming lens 13. In such a case, pixels of the sensor 14 arrange a plurality of rectangular pixels in the longitudinal direction of the finger 15 and also in the direction that orthogonally crosses it, and the length along the direction orthogonally crossing the longitudinal direction of the finger 15 is set so as to be longer than the length along the longitudinal direction. Because of this, in the depth of line rugged parts, an amplitude level is as high as a gray level pixel signal of an image detecting a deep part and is shown with dense tint, and contrast is intensified more than in the case of a fingerprint.