1. A personal identification system comprising: a light source for shining light on a finger of a person to be identified, an imaging device for capturing image of the finger with a blood vein pattern in the finger by the light passing through the finger, and an imaging processing unit for processing image having been captured to acquire a blood vein emphasized image, and for comparing the blood vein emphasized image acquired with an image having been registered to authenticate the person; wherein the imaging processing unit is arranged to authenticate the person by performing calculation of correlation with a monotone increasing calculation in which a calculated output value increases in proportion to degree of matching of two dimensional array elements between the blood vein emphasized image and the image having been registered, and; wherein the imaging processing unit is arranged to acquire the blood vein emphasized image with making an average pixel values of outside and inside of the finger substantially equal.