To automatically perform centering by detecting spatters at work with a spatter detecting means and adjusting and moving a nozzle through a nozzle moving means so that splash of the splatters is homogenized by an adjustment controlling means to the center line of the laser beam. CONSTITUTION:As nozzle holder 3, 4 are moved by the rotation and drive of motors M, M respectively in the direction Y, X and both motors are adjusted and driven by an adjustable amount, the nozzle 5 is adjusted and operated by an adjustable amount of the surfaces X, Y. A beam receiving part 9 for condensing the beam is provided at the lower end of each optical fiber 8 to properly detect the optical amount of the spatters from a work at a focal position of the laser beam LB. The spatter beam is detected properly through the optical fiber 8. Each motor M, M is driven in accordance with a compared result of a comparison device.