PURPOSE: To vary phases of two carriers by nearly 90° simultaneously by controlling a phase of an upper circuit of a phase control circuit externally and allowing a phase of a lower circuit to trace it at a prescribed difference.

CONSTITUTION: An upper circuit of a phase control circuit 4 synthesizes each carrier of phases A,B to generate a carrier whose phase varies linearly from the phase A to the phase B by a CONT voltage and the carrier is outputted through emitter follower Q13. A lower circuit of the circuit 4 synthesizes the phase B and C carriers and the result is outputted from a Q14. The phase of the upper circuit changes toward the phase B and the phase of the lower circuit changes toward the phase C by increasing the CONT voltage. The output carrier of the Q13, Q14 is inputted to a phase detection circuit 5 and an error voltage after passing the filter corrects the CONT voltage of the lower circuit by the output to keep a phase difference between the carriers to be 90°.