To provide a laser beam machining apparatus capable of automatically regulating the focal position of laser beams and regulating the position of laser beams to correct the deviation of the optical axis during the machining.

In the laser beam machining apparatus, a partial reflecting mirror 3 is arranged in the middle between a condensing lens 2 and a machining point. Condensed beams SB condensed by the condensing lens 2 are separated into the condensed beam SB1 for machining and the condensed beam SB2 for monitoring. The focal position of the condensed beam SB2 for monitoring is correctly detected by a focal position detector 4 and deviation of the focal position and the optical axis of the condensed beam SB1 for machining can be regulated to the optimum position by a focal position regulating means 5 and a nozzle position regulating means. The focal position of the laser beams can be automatically regulated, and the optical axis of the laser beams (regulation of the alignment of the nozzle) can be automatically corrected during the machining.