PURPOSE: To quantitatively detect a step out at the time of the acquisition of external field sensor data and internal field sensor data by using only functions that a sensor and a robot basically have by detecting the mean time difference at the time of the acquisition of sensing data and encoder data.

CONSTITUTION: The motion (encoder data) of an actuator 7 is detected by an encoder 8 to be an internal field sensor. A sensor (laser range finder) A fitted to a robot arm B, on the other hand, is an external field sensor and detects position information (sensing data) on a specific position of a working object. This sensing data is sent to a sensor controller 11 and processed, and send into a computer 14 as sending data at a feature point. The computer 14 performs comparative calculation between the internal field sensor and external field sensor to detect the mean time difference at the time of the acquisition of the sensing data and encoder data, and reduces a sensing error in an operation object state on the basis of the time difference.