PURPOSE: To execute engraving which is free from a working misalignment by providing photosensors on the front side and the rear side on a scanning line, relating a moving means to the photosensors and adjusting a detecting position in the forward and backward direction, switching the scanning direction and controlling the timing extending from the pattern detection to the beam irradiation.

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 contact of a first photosensor 3a is closed and a detecting signal is outputted by a black part of a pattern, and a laser beam 7 is outputted. At the time of a main scan in the -X direction, a second photosensor 3b detects a pattern and generates an engraving spot. By repeating the main scan and the sub-scan, the engraving spot is obtained but is becomes a hotched spot a' because the timing extending from the detection to the laser beam irradiation is quick, therefore, when a detecting position of one sensor is set at a distance against the beam irradiated position, a linear spot (a) is obtained. In such a way, the laser irradiation is executed with a good timing, and faithful engraving which follows up a pattern can be obtained.