A measured mark is arranged on a link of an articulated robot. A camera for measuring a position of the measured mark is arranged at a position distant from the articulated robot. A control apparatus of the articulated robot changes posture of the articulated robot, measures positions of the measured mark respectively before and after a change of the posture by the camera, and calculates an actual deflection amount of the link based on a movement amount between the position of the measured mark measured before the change of the posture and the position of the measured mark measured after the change of the posture.