PURPOSE: To improve the reliability as the internal pressure system of an industrial robot by providing a protective circuit not damaging pressure detectors with the pressure at the time of a scavenging action performed before the industrial robot is excited on the pressure detectors.

CONSTITUTION: Pressure detectors 4a, 4b for monitoring the pressure of an internal pressure chamber 2 formed in an industrial robot 100 are provided. A valve 9 is provided between the internal pressure chamber 2 and the pressure detectors 4a, 4b, and the air or inert gas at the time of scavenging is discharged to the outside by the valve 9 not through the pressure detectors 4a, 4b. Even if the pressure for scavenging is set to a value exceeding the allowable upper limit value of the pressure detectors 4a, 4b, the pressure detectors 4a, 4b are not damaged. The reliability as the internal pressure system of the industrial robot 100 can be remarkably improved.