a method of and apparatus for aligning the axis of an assisting gas nozzle with a laser beam axis using a test piece in apparatus which uses a laser to process workpieces is disclosed in which the laser beam is arranged to pass through the assisting gas nozzle , and pierce the test piece . the test piece is held by a holder which includes a pressure detector which measures the pressure of the assist gas flowing through the hold pierced in the test piece . the assisting gas nozzle is adjusted in a plane perpendicular to the axis of the laser beam to obtain a maximum pressure value , which indicates that the axis of the assisting gas nozzle and the axis of the laser beam are in alignment with each other .