To provide a method and a device for precisely detecting shape and darkness of an analyte, even if there exists relatively large rough on the surface.

A line laser marker 11 is set in front of a sidewall part 1 of a tire, and by moving first and second imaging means 12A and 12B provided on the left and right of the line laser marker 11, laser beam 11p is projected vertically on the surface of the sidewall part 1 of the tire. The image, generated by reflected light 11q and 11r from the radiation part, is imaged with the first and second imaging means 12A and 12B, respectively, and the reflected image which has bean imaged is composited by an image-compositing means 13. The composite image, which is the composited reflected image, is image-processed with an image processing device 14, for detecting shape and darkness of the sidewall part 1 of the tire.