| 摘要 |
PROBLEM TO BE SOLVED: To improve convenience in use by reliably confirming a measuring area of a measuring object with simple constitution. SOLUTION: An optical element 15 is a disk-shaped transparent optical prism, and the disk center is fixed to a rotary shaft 16a. Both main surfaces of the optical element 15 are formed of mutually nonparallel crossing planes. That is, a main surface 15a crosses at a right angle to the optical axis L2, and on the other hand, a main surface 15b inclines to the optical axis L2. This optical element 15 is provided with through holes 151 bored in a part of an area to pass the beam light 13a from a light emitting part 13, that is, in a part on the circumference of a radius equal to a distance between the rotary shaft 16a and the optical axis L2 with the rotary shaft 16a as the center. When the optical element 15 is rotated, a ring image 41a to show the contour of a measuring area and a spot image 41b to show the measuring center are displayed.
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