PURPOSE: To execute engraving which is free from a working misalignment by operating a detecting position switching means of a photosensor in relation to the scanning direction, detecting a laser beam irradiated position, delaying a detecting output and outputting it to an irradiation control circuit.

CONSTITUTION: A body 2 to be scanned and a material 4 to be worked are attached onto an X.Y table 1, and thereafter, the table 1 is driven. At the time of a main scan in the +X direction, a photosensor 3 is positioned in the front side by a detecting position switching means and a detecting signal is outputted by a black part of a pattern (a), and after a set time of a delaying circuit elapses, a beam 7 is outputted. After a sub-scan in the +Y direction, a main scan in the -X direction is executed, and the photosensor 3 positioned in the rear side detects and outputs the pattern (a). These main scan and sub- scan are repeated and a notched spot a' appears. It occurs because the irradiation timing is quick, therefore, by lengthening a delay time of the delaying circuit, a linear engraving spot (a) can be obtained exactly. In such a way, the laser irradiation is executed with a good timing and faithful engraving which follows a pattern can be obtained.