PURPOSE: To easily select the position, number, size, etc., of piercing by moving a tube held in a cylindrical state in the longitudinal direction and forming focuses of a laser beam at prescribed intervals on the side of the tube to perform piercing in order.

CONSTITUTION: The tube 1 is held in the cylindrical state. This tube 1 is moved in the longitudinal direction and the tube side is irradiated with the laser from a laser beam irradiation part 3 and the focuses of the laser beam are formed at the prescribed intervals on the side of the tube 1 to perform piercing in order. At the time of forming the tube, carbon black is dispersed at the rate of ≥0.5weight%. The laser beam is emitted from a laser beam generator which condenses excitation light on an excitation body containing YAG and emits near infrared rays. Gas is sent in the tube. By this method, piercing can be performed on the accurate positions and mass production can be also executed satisfactorily.