Abstract: A saddle 18 is movable along a guide means 16 provided, passing through an neighborhood of machining area MA of a plurality of machine tools 1, 2. The saddle 18 is provided with a machining head 33, being free to selectively insert in and retreat from the machining area MA, and a plurality of kinds of nozzles 48 for ejecting laser beam. The nozzle 48 suitable for a portion of workpiece 3, 4 to be hardened is selected so as to attach it to the machining head 33. When hardening is instructed, the nozzle 48 is moved to a desired position with respect to the workpiece 3, 4 in the state of the workpiece 3, 4 located on the machine tool 1, 2, and the laser beam 51 is ejected from the nozzle 48 so as to harden the workpiece 3, 4.