This biometric authentication device uses a finger authentication prism that has a trapezoid shape when viewed from the side and is provided with: a finger mounting surface on which a finger to be authenticated is placed an imaging surface that is arranged to face the finger mounting surface in parallel and a reflection surface that is positioned at a prescribed angle relative to the finger mounting surface and the imaging surface such that, subsequent to irradiated light being reflected by the finger mounting surface, the irradiated light is totally reflected and reaches the imaging surface. When the imaging surface of the finger authentication prism is exposed to visible light and/or infrared light, the light reflected by the finger placed on the finger mounting surface is branched between a first light path that reaches the imaging surface directly, and a second light path that reaches the imaging surface from the finger mounting surface via the reflection surface. From amongst the reflected light that has traveled the first light path and the second light path, the biometric authentication device forms a first image on the basis of the reflected light corresponding to a region of the finger extending from the distal interphalangeal joint in the fingertip direction, and forms a second image on the basis of reflected light corresponding to a region of the finger extending from the distal interphalangeal joint in the finger-base direction.Linvention concerne un dispositif dauthentification biométrique utilisant un prisme dauthentification de doigt qui a une forme trapézoïdale lorsquil est vu sur le côté et comportant : une surface de montage de doigt sur laquelle un doigt devant être authentifié est placé une surface dimagerie qui est agencée de manière à être orientée vers la surface de montage de doigt de manière parallèle et une surface de réflexion qui est positionnée au niveau dun angle prescrit par rapport à la surface de montage de doigt et la surface dima
