1. A biometric authentication device, for verifying at least a biometric on a portion of a creature to be verified (PTBV), the PTBV comprising at least a portion of a first finger member and a second finger member of a finger, said biometric authentication device comprising: a carrier base, having an upper opening for receiving at least the first finger member and the second finger member of the PTBV, which the upper opening further has a base plane and at least one lateral surface; a position structure, located at the carrier base at a position respective to the upper opening, used to assist the PTBV to anchor at a predetermined position at the carrier base in the upper opening; at least one light source unit, located at the at least one lateral surface of the carrier base respective to the upper opening; in the case that the PTBV reaches the predetermined position, the at least one light source unit positioned laterally to the PTBV, and the at least one light source unit projects at least one lateral light onto the PTBV such that said lateral light penetrates both the first finger member and the second finger member of the PTBV to generate a fingerprint image and a vein image respectively corresponding to the first finger member and the second finger member of the PTBV; a light guide module, located inside the carrier base at a position under the base plane respective to the upper opening; and an image-sensing unit, located inside the carrier base to receive both the fingerprint image and the vein image and further to form thereby a corresponding detection signal readable to a computer; both the fingerprint image and the vein image entering the carrier base through the base plane of the upper opening and projected onto the image-sensing unit via the light guide module; wherein the fingerprint image is generated by having the lateral light penetrating the first finger member, while the vein image is generated by having the lateral light penetrating the second finger member; wherein the light guide module is separated into a fingerprint-detecting area and a vein-detecting area; the fingerprint image formed on the image-sensing unit through the fingerprint-detecting area of the light guide module, the vein image formed on the image-sensing unit through the fingerprint-detecting area of the light guide module; wherein the first finger member contacts a top surface of the fingerprint-detecting area in order to generate the fingerprint image when the lateral light penetrates the first finger member and the second finger member is located above but does not contact another top surface of the vein-detecting area in order to generate the vein image when the lateral light penetrates the second finger member; wherein, when the at least one lateral light penetrates the PTBV, the fingerprint image and the vein image are formed simultaneously on the image-sensing unit through the fingerprint-detecting area and the vein-detecting area of the light guide module, respectively, and then the image-sensing unit generates the detection signal readable to the computer and has messages of the fingerprint image and the vein image; wherein the position structure is formed as a finger-anchoring structure located on the base plane and further includes a front window, a rear window and a position rib between the front window and the rear window; while an inter-member valley between the first finger member and the second finger member falls onto the position rib, the first finger member is anchored in the front window and the second finger member is anchored in the rear window; and the fingerprint-detecting area is respective to the front window and the vein-detecting area is respective to the rear window; and wherein the light guide module has one single prism unit separated into the fingerprint-detecting area and the vein-detecting area; the fingerprint-detecting area of the prism unit further includes the top surface, a bottom surface opposing to the top surface, an imaging surface connecting in-between the top surface and the bottom surface, and an anti-reflection surface opposing to the imaging surface, the top surface neighboring the front window of the position structure; when the PTBV is anchored at the predetermined position in the upper opening, the first finger member of the finger contacting the top surface of the fingerprint-detecting area, the fingerprint image entering the fingerprint-detecting area of the prism unit via the top surface of the fingerprint-detecting area, the fingerprint image reflected at least once by the bottom surface of the fingerprint-detecting area and then leaving the prism unit through the imaging surface of the fingerprint-detecting area, an oblique angle of the imaging surface of the fingerprint-detecting area causing the leaving fingerprint image to form on the image-sensing unit, the anti-reflection surface reducing the reflection; and the vein-detecting area of the prism unit further includes said another top surface, another bottom surface opposing to the another top surface, another imaging surface connecting in-between the another top surface and the another bottom surface, and a reflection surface opposing to the another imaging surface and forming an oblique angle with the another bottom surface; said another top surface of the vein-detecting area neighboring the rear window of the position structure; when the PTBV is anchored at the predetermined position in the upper opening, the second finger member of the finger being above said another top surface of the vein-detecting area without any contact in between, the vein image entering the vein-detecting area of the prism unit via said another top surface of the vein-detecting area, the vein image reflected at least once individually by the reflection surface, said another top surface and said another bottom surface of the vein-detecting area, and then leaving the prism unit through said another imaging surface of the vein-detecting area, the oblique angle of said another imaging surface of the vein-detecting area causing the leaving vein image to form on the image-sensing unit; an imaging optical path of the vein image depending on a vertical height between said another top surface and said another bottom surface of the vein-detecting area and a reflection frequency of the vein image inside the vein-detecting area, in which the reflection frequency is determined by the oblique angle between the reflection surface and said another bottom surface of the vein-detecting area.