A motor control system capable of outputting motor control data contained in a numeric control device and inputting motor control data to the numeric control device as required, without using a proprietary connector and/or a switching unit. The control system has a numeric control device, a plurality of motor amplifiers for receiving a command from the numeric control device via a serial communication line, a plurality of motors such as servomotors each driven by each of the plurality of motor amplifiers, and a data I/O device for inputting and outputting motor control data, as analog data or digital data, included in software in the numeric control device. The data I/O device may also transmit motor control data, to the numeric control device, as analog or digital data.