PURPOSE: To secure the reliability of an angular displacement detection value in a galvanoactuator moving part and to improve stability in two stage servo control by adjusting a liner area a tilt senser output to match a rotation range in the galvanoactuator.

CONSTITUTION: Luminous flux from the light emitting diode of the tilt senser 8 in a tilt senser mechanism 6 is reflected by the reflection plate 9 of the galvanoacturtor moving part 5, and by a relative current difference value obtained from the light quantity of a spot forming an image on a bi-sected photodiode, an angular displacement in the actuator 5 is detected. In such s case, since the output value of the tilt sensor 8 according to the position of the moving part 5 is nonlinear, it is necessary that the moving part 5 is rotated in the linear area. Thus, an adjustment screw 146 is provided in the tilt senser mechanism part, and by adjusting inclination, the liner area is matched the rotation range in the moving part. Thus, the reliability of the angular displacement detection value in the galvanoactuator moving part is secured, and the stability in servo control is enhanced.