A fake finger in which a transparent thin film is attached to a finger surface is discriminated. A fake-finger determination device includes: an imaging unit 10 that captures an authentication object as a fingerprint authentication object; a classifying unit 31 that classifies an image captured by the imaging unit 10 into a plurality of regions including at least a skin region and a background region using colors of pixels included in the image; and a determining unit 32 that determines whether or not a foreign substance is present in the periphery of a finger based on a feature of a region classified as neither the skin region nor the background region out of the regions classified by the classifying unit 31.