PURPOSE: To obtain a small size and compact encoder by reducing the number of bits of the absolute signal in a rotation.

CONSTITUTION: By the original point return signal from a driver system to a Zn signal, a motor drives and rotates from A point to CW direction, the position changes to B point and original point return operation is completed and then comutation data, Zn zone data and multiple rotation count data at point B as well as point A are sent to a driver system by way of a transmitted data switching circuit 16 and a conversion circuit 17. In the driver system, the mode is selected to add the counted value at A and B phases besides the one rotation absolute data as the representative of the past. And then on, the one rotation absolute data are renewed by the change of the A and B phases in this mode. As the one rotation absolute data changes at this moment with the resolution of 1/1000 in the driver side, the comutation data signal is changed to sine wave and the motor is driven with the sine wave drive.