Abstract: The present invention is a thickness measurement device which allows high-speed, high precision and stable measurement with a simple configuration and with easy maintenance. A coherent light emitted from a light source 31 is transformed to a desired linearly polarized light by a polarizer 32, this linearly polarized light is entered into a test object 33 having double refraction, a normal beam and an abnormal beam are extracted, the extracted beams are entered into a wedge prism 34, and a beam which transmit through the measurement location of the test object 33 and has the phase difference which changes according to the total thickness of the test object 33 and the wedge prism 34 are extracted.

Abstract: When mounting crystal blanks, crystal blanks can be mounted readily in a desired position on a mounting platform, and during pick-up, they can be readily detached from the mounting platform. To inspect scratches in a crystal blank 1, diffused oblique light is shined onto the crystal blank 1 from below by light-emitting diodes 6, and light reflected by scratches on the crystal blank 1 is detected by image capturing means 11 directly above the crystal blank 1. The crystal blank 1 is conveyed to the mounting platform 2 by a conveyor robot arm 15, and after inspection, it is conveyed away by same. A plurality of grooves are formed in the mounting surface 3 of the mounting platform 2. Thereby, during mounting, the crystal blank 1 does not slide over the mounting platform 2 and after mounting, it does not adhere tightly to the mounting platform 2.