To prevent the pollution caused by the heat of an optical parts by the heat at a low cost by allowing the temperature of the optical parts being the components to be lower than the evaporation temperature of the optical parts.

A laser beam device, in particular, a laser beam machine is provided with at least one optical parts which is arranged in an optical path of the laser beam 5 and allows the laser beam 5 to transmit at least partially, for example, at least one output lens 6 and/or at least one converging lens 8. The laser beam device is provided with optical parts 6, 8, a temperature detector to detect their temperature, and a detector of the intensity of the laser beam emitted by the optical parts 6, 8. The laser beam is controlled so that the temperature of the optical parts 6, 8 is adjusted according to the intensity of the detected laser beam.