A laser machining device includes a laser emitting device, a supporting device including a supporting surface, a controller, and optical detecting units mounted on the supporting surface. The laser machining device sets an X-Y coordinates having an original point and moves to being substantially above one of the optical detecting units. A laser beam is emitted at a plurality of microscopically-close positions and the values of the luminous flux of the received laser beams are detected, the values being sent to the controller. The controller compares the detected values to determine the greatest value, and corrects the position of the original point to accord with the position of the greatest detected value.