PURPOSE: To execute measurement and marking at the same place and to improve production efficiency by detecting the work supported to a supporting device by a detecting mechanism, measuring the size thereof and marking the size as it is to the work.

CONSTITUTION: The outside size of the object to be measured is calculated by WX=W1+W2+W3 by using the distance W1 between optical sensors 30 and 30 when the widths W2, W3 of the parts of parallel rays 39, 39 shielded by both ends 3a, 3b of the work 3 are detected by the sensors 30, 30. The size of the work 3 obtd. in the above-mentioned manner is converted to the code for marking the size by a laser marking device 1 and the code is fed to the device 1, by which the code is marked to the work 3.