1. An individual authentication device for authenticating an individual using feature information of a vascular pattern acquired from a living body, comprising: an imaging unit that images a region of the living body serving as an object of authentication; and an arithmetic unit that acquires one picked up image including the vascular pattern imaged by the imaging unit as an authentication image, wherein the arithmetic unit extracts a plurality of feature points in the vascular pattern of the one picked up image, each of which exhibits a predetermined feature, on the basis of luminance of the authentication image, the arithmetic unit calculates positional information of each of the feature points in the vascular pattern and a difference in the luminance between the feature points, and acquires the positional information and the difference in the luminance as the feature information, the arithmetic unit acquires luminance levels of the respective feature points as pieces of depth information attributable to the shape of the vascular pattern in a direction perpendicular to a plane on which the authentication image is formed, the arithmetic unit extracts pieces of information, which are based on the interrelationships in the perpendicular direction of the respective feature points, from the pieces of depth information, and the arithmetic unit acquires the pieces of information as pieces of feature information relevant to the respective feature points.