| 摘要 |
PROBLEM TO BE SOLVED: To enhance the efficiency of measuring operation by a constitution, wherein a focus direction means detects the focusing state of an optical-pickup objective lens, an adjusting means changes the distance between the objective lens and an image detection means according to a detection signal, and the objective lens is focused. SOLUTION: Light which is extracted by a light splitting element 8a, which is arranged in an optical path between the microscope optical system 5a and an image input device 5b of an image detection means 5 is detected by a position detection means 8, as a beam spot image which passes through the objective lens 10 of an optical pickup 1 and a dummy disk 6 and which is magnified by the optical system 5a. Positional information on the horizontal direction with reference to the optical system 5a of the optical pickup 1 is detected. In addition, the position detection means 8 selects in advance the area of the position detecting element 8b of the position detection means 8 or the optical magnification of a lens 8c used to condense light from the light splitting element 8a on the detecting element 8b, in such as way that it has a visual field which is several times that o the image detection means 5. Therefore, even if the spot image is deviated from the visual field of the image input device 5b, the position of the spot image can be detected by the detection means 8, and the spot image can be positioned inside the visual field of the image input device 5b.
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