A pressure of a laser gas in an enclosure (7) is detected by a gas pressure sensor (12), and a pressure comparison circuit (13) determines whether the thus-detected pressure is normal or anomalous. An electric current output from an inverter (10) that drives a blower (5) to cause a laser gas to flow back, is detected by a current detection circuit (9). A current comparison circuit (11) determines whether or not the output current is normal or anomalous. A result of a pressure comparison circuit (13) and a result of the current comparison circuit (11) are sent to an AND circuit (15) and performed AND processing. A result of the AND circuit (15), a result of the current detection circuit (9), and a result of the gas pressure sensor (12) are sent to a comparison operation section (17) in a controller (14). A determination is made as to whether or not the blower is anomalous. When the blower is determined to be anomalous, a signal is output to an oscillator and a machine control section (18), to thus stop the oscillator and the machine. Thereby, an anomaly in the blower (5) can be detected regardless of fluctuations in the pressure of the laser gas.