PURPOSE:To improve control accuracy and stability by providing a means correcting slippage from standard position of a laser beam scanned by a galvanometer type scanner to a laser beam scanner. CONSTITUTION:In the case of executing the standard position correction, light 14 is turned off by a motion control device 5 through a scanner control circuit 16, and the standard light source 15 is turned on. After this standard light passes a dichroic mirror 12, it passes a lens 11 and a mirror 17 through scanning mirrors 10, 8 controlled to the standard rotating angle and is condensed by a lens 18. It is imaged by a video camera 19 and inputted to a standard position detecting circuit 20 as a video signal. After that, the video signal 204 of the position of standard light is compared with the comparing level 203 (not shown) by a comparator 301 and detected as a standard position signal 205 (not shown), and information of the position of standard light is extracted. The slippage of the detected valve from the standard value is calculated and corrected by the motion control device 5, the corrections of the scanning position, besides the position coordinate of the laser beam, are executed.
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