PURPOSE: To provide a uniform welding width over the full area to be welded by substantially eliminating the delay in operation of a laser beam oscillator to a machining head.

CONSTITUTION: A machining head 2 is directly controlled by a control device 10 while a laser beam oscillator 1 is controlled by the control device 10 through an oscillator control means 11. Thus, the operation of the laser beam oscillator 1 is delayed to the machining head 2 by the degree corresponding to the operation through the oscillator control means 11. A welding mode 15 is added to the control device on the assumption of the laser beam machining equipment for general purpose. When a work 4 is welded by a welding mode 15, the machining head 2 is moved simultaneously with the irradiation of the laser beam L at the welding starting position A, while the machining head 2 is stopped simultaneously with the stopping of the irradiation of the laser beam L in the welding comleting position B.