| 摘要 |
PROBLEM TO BE SOLVED: To obtain a focus error always and stably even when irradiating positions of light spots on an optical disk are changed. SOLUTION: The first photodetector 14 of this light transmitting and receiving device receives the reflected light of a light spot formed on, for example, a land and second and third photodetectors 16, 17 of the device receive reflected lights of light spots formed on grooves of both sides of the land. Then, first to third error calculating means 20, 22, 24 calculate focus errors of respective light spots using signals which are to be outputted respectively by the first to third photodetectors 14, 16, 18 and a fourth error calculating means 26 calculates a focus error by totalizing the focus error which are calculated respectively by the first to third error calculating means 20, 22, 24. Then, the distance between an objective lens 8 and an optical disk 114 is controlled based on the focus error calculated by the fourth error calculating means 26.
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