To provide a marking data device and its working method by which good-quality marking whose working depth is small and where soot is made little is easily worked at high speed, for example, in the marking for an IC package, etc.

In this laser marking device and its working method, marking is performed so as to simultaneously scan a worked surface by arranging plural thin laser beams to line up in series by a laser divider 4 and external switches 5 and 6 based on specified image data previously recorded in a CPU 1, and individually outputting and controlling plurally divided thin laser beams while scanning in a direction orthogonal to the line of the laser beams by galvanometers A8 and B9 and an fθ lens 10 with the N-laser beams scanning.