In a laser beam machining method in which laser beams L are irradiated with a movement of the robot 3 and the three-dimensional workpiece 10 is machined, a locus speed of the robot 3 at a position where the workpiece 10 is machined is measured previously or in real time, and an intensity of the laser beams is controlled according to this locus speed. In the case of a workpiece made of resin, in addition to the locus speed, a change in the transmission of the workpiece with respect to the laser beams is fed back to an output of the laser beams.