To precisely mark while controlling a dot diameter and a marking depth to an arbitrary value.

Based on the characteristic table prepared beforehand, marking is performed while adjusting a laser beam oscillator, laser beam attenuator, laser beam expander, etc. A shot number of a laser beam in the laser beam oscillator is adjusted with referring the characteristic table showing the relation between a marking depth and a shot number (step 2-2), the laser power in the laser beam attenuator is adjusted with referring the characteristic table showing the relation between a dot diameter and power (step 2-4), a magnification in the laser beam expander is adjusted with referring the characteristic table showing the relation among a dot diameter, a marking depth and a beam diameter (step 2-5).