A laser beam machine for machining a workpiece by moving a workpiece attached to a table and an optical head, configured to irradiate a laser beam, relatively to each other, and irradiating the laser beam to the workpiece, the laser beam machine comprising: a table with a calibration unit; an optical head configured to irradiate a laser beam to a workpiece; an optical sensor secured to the optical head; characterized by a touch probe secured to the optical head; and the calibration unit comprising a calibration ring assembly including a cylindrical body configured to provide a measurement reference for the probe, a flange part radially inwardly extending from the cylindrical body to provide a measurement reference for the optical sensor, and a plate providing a to-be-processed part configured to be removably inserted into the body; wherein the cylindrical body and an inner surface of the flange part are formed so as to be concentrically aligned with each other; wherein the plate is adapted to be machined by the laser beam to form a machined mark (L1, L2); wherein the optical sensor is configured to measure the position of the machined mark (L1, L2) on the to-be-processed part and the position of the measurement reference along an inner periphery of the flange part of the calibration unit; wherein the probe is configured to measure the position of the measurement reference along an outer peripheral surface of the cylindrical body of the calibration unit; and wherein the laser beam machine is configured to calculate the deviation between the position of a machining point of the laser beam and the position measured by the probe, based on the position of the machined mark and the position of the measurement reference, measured by the optical sensor, and the position of the measurement reference measured by the probe, obtain the relative position between the workpiece and the machining point of the laser beam, based on the calculated deviation between the machining point of the laser beam and the position measured by the probe, and the position of the workpiece measured by the probe and machine the workpiece by moving the table and the optical head relatively to each other, based on the obtained relative position between the workpiece and the machining point of the laser beam. a table with a calibration unit; an optical head configured to irradiate a laser beam to a workpiece; an optical sensor secured to the optical head; characterized by a touch probe secured to the optical head; and the calibration unit comprising a calibration ring assembly including a cylindrical body configured to provide a measurement reference for the probe, a flange part radially inwardly extending from the cylindrical body to provide a measurement reference for the optical sensor, and a plate providing a to-be-processed part configured to be removably inserted into the body; wherein the cylindrical body and an inner surface of the flange part are formed so as to be concentrically aligned with each other; wherein the plate is adapted to be machined by the laser beam to form a machined mark (L1, L2); wherein the optical sensor is configured to measure the position of the machined mark (L1, L2) on the to-be-processed part and the position of the measurement reference along an inner periphery of the flange part of the calibration unit; wherein the probe is configured to measure the position of the measurement reference along an outer peripheral surface of the cylindrical body of the calibration unit; and wherein the laser beam machine is configured to calculate the deviation between the position of a machining point of the laser beam and the position measured by the probe, based on the position of the machined mark and the position of the measurement reference, measured by the optical sensor, and the position of the measurement reference measured by the probe, obtain the relative position between the workpiece and the machining point of the laser beam, based on the calculated deviation between the machining point of the laser beam and the position measured by the probe, and the position of the workpiece measured by the probe and machine the workpiece by moving the table and the optical head relatively to each other, based on the obtained relative position between the workpiece and the machining point of the laser beam.