It is determined whether the first tool identification information that is output from a robot control device, and that indicates a present tool and the second tool identification information for detecting and identifying a tool attached to the robot are unequal to each other. The position coordinates of the taught reference point in an actual space of the robot occurring at the time when the unequalness therebetween is first detected are set as reference coordinates, and a region that contains the reference coordinates is set as a predetermined region. If the position coordinates of the taught reference point have come to exist outside the predetermined region during a period during which it is determined that the foregoing two pieces of information are unequal, an emergency stop signal for causing the robot to be in a safe state is output.