DETECTION METHOD OF DISCRIMINATION MARK

PROBLEM TO BE SOLVED: To efficiently detect a discrimination mark by a constitution wherein each of the discrimination marks comprises a regulation reflection section that reflects a light having a predetermined regular wavelength. SOLUTION: Each of discrimination marks 1, 2...m on an optical passage comprises a regulation reflection section that reflects a light having a predetermined regular wavelength λ1. When the light having the wavelength λ1 is incident thereon as a position observing light, reflection lights are obtained from all of the discrimination marks. At that time, phase differences Δt1, Δt2,...Δtm (time intervals) between the incident lights and reflection lights are measured so that positions of the respective discrimination marks on the optical passages are observed. The inspection light having a wavelength (for example λ2) corresponding to one of the reflection sections is allowed to enter the optical passage. It is judged whether or not the reflection light is detected by each of the phase differences Δt1, Δt2,...Δtm. When the reflection light of the inspection light having the wavelength λ detected by a certain phase difference, it is determined that the discrimination mark corresponding to the phase difference has the reflection section that reflects the light with the wavelength λ2.