To obtain a laser machining method and device capable of high precision and highly efficient machining using CO2 or Nd:YAG laser.

A laser beam 2 from a laser generator is reflected by a reflection mirror and converged on a work 4 by a condensing lens 3. An XY table 5 is moved in the X direction by the X stage driving part 5xd on a command from the X stage controller 5x and, similarly, the XY table 5 is moved in the Y direction by the Y stage driving part 5yd on a command from the Y stage controller 5y. An ultrasonic vibrator transducer 6 is arranged in a position facing the work 4 surface opposite to the one irradiated with the laser beam, and is driven by a driving part 6d in accordance with a command from the controller 6c of the ultrasonic vibrator transducer 6. The controller 6c controls the transducer 6 through the driving part 6d so that an ultrasonic wave is emitted to the stress concentrating zone in the cutting part of the work 4. An elastic stress generated by the ultrasonic wave is superimposed on a thermal stress generated by the laser beam 2, thereby increasing a stress expansion coefficient.