PURPOSE: To contrive to decrease a cost by reducing the number of wirings between an encoder and a servo controller.

CONSTITUTION: When the exclusive OR of Z'-signal taking the AND of A-phase signal Ain being two-phase signal and Z-phase signal Zin being origin signal by AND gate 3 and B-phase signal Bin being two-phase signal is taken by EOR gate 4, the B-phase signal is overlapped by the Z-phase signal and transmitted, the rise and fall of transmission signals A', B' are detected by D-FFs 5, 6 and EOR gates 7, 8, and the AND of the output of the EOR gates 7, 8 is taken by AND gate 9. Further, when the A'-signal is latched by that output, Zout-signal equivalent to the Z-phase signal Zin is extracted and a signal wire for transmitting the Z-phase signal becomes useless.