PURPOSE: To provide a miniature encoder having reduced number of output wires with low cost and to facilitate the wiring work when an AC synchronous motor is started through the encoder.

CONSTITUTION: A conventional encoder outputs two phase signals A and B, an original point signal Z, and pole position signals (U, V, W), i.e., total six types of signals. In the invention, a ZP signal where the pole position signal is superposed on the original point signal is generated in addition to the two phase signals A and B thus outputting total three types of signals. Consequently, the number of wires is decreased and a downsized encoder can be fabricated with low cost while furthermore wiring work to a controller can be facilitated when an AC synchronous motor is started.