1. A vehicle identification method comprising the steps of: taking an image frame of a vehicle by an interlace method; performing irradiation in an odd field and an even field composing the image frame with light of light quantities different from each other; capturing images of the odd field and the even field; and performing character recognition processing, only when character recognition processing of a number plate area extracted from an image of one field has ended in failure, of a number plate area extracted from an image of the other field.