Provided is a small-sized, flat, vein authentication device of high authentication accuracy by photographing a living body several times and thus obtaining as registration data plural images that are picked up at different positions. A biometric information processing device of this invention comprising an image pickup device, which picks up a vein image, an image computing unit, which processes the vein image picked up by the image pickup device, an interface on which a part of a living body to be picked up is placed, and a light source, which emits infrared light. The biometric information processing device is further comprised of a sensor unit, which detects the presence or absence of a subject picked up by the image pickup device, a unit to obtain plural images as registration data, and a unit to select optimum registration data out of images obtained as registration data.