PURPOSE: To judge the performance of a sensor by obtaining the offset quantity from the first load vector determined from the known mass and the center of gravity position in the first attitude and the first load data detected by the sensor, and obtaining the error between the second load vector determined likewise in the second attitude and the second load data subtracted with the offset quantity after detection.

CONSTITUTION: A robot main body 1 fitted with a member 10 is set to one attitude, and the center of gravity position and the mass of the member 10 are known. A controller 6 calculates the load vector passing through the center of gravity position of the member 10 from the information, receives the load data detected by a force sensor 5, and determines the offset quantity of the sensor 5 from both data. The robot main body 1 is set to another attitude, the load vector is likewise calculated, and the previously determined offset quantity is subtracted from the load data detected by the sensor 5. The error between it and the load vector is obtained, and the error value is displayed on the display device 9a of an operation section 9. The detecting performance of the sensor 5 can be inspected by this magnitude.