PURPOSE: To realize an orthogonal modulation signal with high accuracy used for a wide band carrier frequency from a simple circuit.

CONSTITUTION: The orthogonal modulation circuit is provided with a frequency synthesis circuit 5 outputting a carrier signal, modulation carrier signal generating means 6, 7, 81, 82, 91, 92 outputting two modulation carrier signals of opposite phase, two phase modulators 31, 32 modulating a modulation carrier signal in terms of phase by using 2-series of data signals and a signal synthesis circuit 4 synthesizing the two signals subject to phase modulation. Furthermore, the circuit is provided with a phase shifter 82 correcting an orthogonal phase error different from the frequency and a phase control section 10 receiving part of the carrier signal from the frequency synthesis circuit 5 and outputting a control signal of a level inversely corresponding to the orthogonal phase error.