| 摘要 |
PURPOSE:To prevent the influence due to secular change of parts, by moving a position of a photodetector to an optimum position in accordance with the magnitude of a signal of the photodetector. CONSTITUTION:A light beam emitted from a semiconductor laser 31 is made incident to a photodetector, and is inputted to a photodetector position control part 39 through a recording signal reproducing part 36, a rectifying circuit 37 and an A/D converting circuit 38. By a photodetector moving part 40, the photodetector 34 is moved in the direction where a reproducing signal is obtained in an optimum state, and so as to negate it, the focus control is executed by a focus control part 35. In this way, since a signal output of the photodetector is controlled so as to be optimum, the reproduction is executed in a stable state irrespective of secular change of parts. |
