PURPOSE: To reduce the maintenance cost due to the pollution and breakage in achieving the laser beam machining by separating the multiple dividing function of the laser beam from the converging function to facilitate the manufacturing of individual optical parts such as a reflecting mirror and a converging lens and to reduce the cost.

CONSTITUTION: The laser beam B1 emitted from a laser beam oscillator through a transmission system is multiply divided (two in the illustration) by a flat type reflecting mirror 3 within a machining head 1, and the respective laser beams b1, b2 are reflected by another reflecting mirror 4 consisting of a single parabolic mirror to be converged to the focal points P1, P2 distributed on a work W in the transverse direction. The reflecting mirror 3 consists of two semi-circular mirrors 3a, 3b capable of changing the inclination of the surface.