An image taking unit having a lens array, a light shielding member, and an image taking unit that acquires a compound eye image of a vein pattern of a living body held at a lens array. A shift estimation unit estimates an image shift amount between ommatidium images of the compound eye image. An image restructuring unit restructures a single image from the compound eye image by using the image shift amount. A size correction unit corrects the size of the restructured single image with a magnification ratio determined by the estimated image shift amount and an image shift amount stored in a registration pattern storage unit so as to correspond to a registration pattern. As a result, it is possible to perform personal authentication while compensating influences due to fluctuations in a subject distance.