BEAM POSITION CONTROLLER

PURPOSE:To eliminate the influence of disturbance such as temperature variation and vibration providing an oscillator and a control switch in a beam position control circuit. CONSTITUTION:The oscillator 8 is oscillated with an initializing signal to move movable reflectors 4a and 4b, and thus beams 5a and 5b are deflected and become easy to strike a photodetector, which detects the beams 5a and 5b to perform servo control. Phase advancing circuits 33 and 34 which compensates the phase delay in sample holding circuits 35 and 36 are provided to compensated the phase delay. Position errors of the individual detectors and characteristic errors in manufacture are adjusted by voltage adjusting means 27 and 28, so beam positions can accurately by adjusted. The phase delay circuits 35 and 36 for a low frequency range are provided to improve the gain in the low frequency range, so shifts of the beam positions can be suppressed.