To precisely read a mark without being influenced by means of disturbance by using a linear light beam for photographing the unevenness of the surface of an object.

A laser projection device 4 projects the linear light beam on the mark 3 on the surface 2 of the object 1 from above or from obliquely above. The linear light beam is that by which the irradiation part of light forms a linear line on the surface of the object. An image pickup device 7 takes the surface of the object 1 which is irradiated with the light beam of the projection device 4 from obliquely above or from above. A moving device 11 relatively moves the projection device 4 and the image pickup device 7 to a direction rectangular to the linear light formed on the object 1. The object 1 moves to the direction of an arrow A. An arithmetic processing unit 15 judges the presence of the unevenness of the surface 2 of the object 1 from image pickup data of the image pickup device 7 and generates data of unevenness. Since the unevenness of the mark is directly measured by the stable light source of laser beam, unevenness can precisely be discriminated and the mark can be identified without being affected by disturbance light except for laser beam.