PURPOSE: To prevent production of a false signal caused at the leading and trailing of a PN signal by using the PN signal so as to modulate an FM modulation wave after the leading and trailing generating timing of the PN signal is made coincident with a zero cross pulse.

CONSTITUTION: A zero cross pulse generating means 5 generates a zero cross pulse at a zero point of an FM modulation wave being an input signal and a timing revision means 8 makes the leading and trailing timing of the PN signal coincident with the generating timing of the zero cross pulse. Succeedingly, a balance modulation means 9 uses a P signal to modulate the FM modulation wave. Thus, no discontinuous signal is generated in a square output at FM demodulation.