1. A finger vein authentication apparatus comprising: a lens array including a plurality of photo-receiving lenses arranged in an array; a plurality of near-infrared illumination sources placed along opposed ends of the lens array to illuminate a part of a finger with near-infrared light; an image pickup device to create a picked-up image of a vein based on the near-infrared light scattered inside the finger, transmitted through the vein and gathered by the lens array, the image pickup device creating two kinds of picked-up images by performing line scanning in both of a first direction along an alignment direction of the near-infrared illumination sources and a second direction orthogonal to the first direction and along a lengthwise direction of the finger; a vein pattern extraction unit to extract vein patterns respectively from the two kinds of picked-up images; an authentication unit to authenticate the extracted two kinds of vein patterns; and an imaging range detection unit to detect a relative position of an imaging range of the finger by using at least one of a crease pattern near a first joint and a crease pattern near a second joint of the finger existing in at least one of the two kinds of vein patterns.