A safety unit is provided for this purpose, and includes a position determining unit, a speed determining unit, a logical product unit, and a stopping unit. When a rotation amount (positional data) of an encoder rotating in connection with a rotation shaft of a servo motor falls within a predetermined limiting range, the position determining unit outputs a command for stopping a motor to a logical product unit. When rotation speed of the encoder rotating in connection with the rotation shaft of the servo motor falls within a predetermined limiting range, the speed determining unit outputs the command for stopping the motor to the logical product unit. This control by the logical product unit requires a stop command from both the position and speed determining units. The logical product unit informs the stopping unit to stop the servo motor to a controller.