PURPOSE: To make the reliability of wiring higher by reducing the number of signal lines for the encorder signal in a servomotor.

CONSTITUTION: A speed detecting means 13 for producing the speed data from an encorder signal, a position detecting means 14 for producing a position data from the encorder signal, a serial signal transmitting means 15 for converting these speed and position data into a serial signal, and a line driver 16 for transmitting and outputting this serial signal, are provided in the encorder 11 of a servomotor. And the serial signal transmitted from this line driver 16 is received by a line receiver 19 in a driver 17. Furthermore, the serial signal received is converted into a speed data and a position data by a serial signal receiving means 20 and outputted. And speed and position control are performed on the basis of these output data.