PURPOSE: To enable the accurate angle aligning of an optical axis and a moving axis, and to relax the mechanical accuracy of a device by providing a two-focus lens, and adjusting the position of a light source so that two image forming positions appearing on an observation face at the time of moving a conveying means can be coincident.

CONSTITUTION: A composite Fresnel zone plate 101 having two focuses F1 and F2 on the same axes is arranged at an actuator part 13, the two image forming positions appearing on an observation face 104 at the time of moving the actuator part 13 are observed by a TV camera 102 or the like, so that an angle deviation of the optical axis of the outgoing beams of a fixing part 12 and the moving axis of the actuator part 13 can be detected. Then, the position of a light source 26 is adjusted so that the two image forming positions can be coincident. Thus, the outgoing optical axis from the fixing part 12 and the moving axis of the actuator part 13 can be efficiently adjusted with a necessary and sufficient accuracy, and the mechanical accuracy of the device can be eased.