PURPOSE: To obtain a serial communication circuit which dispenses with adjustment of a frequency, and also, can lower power consumption at the time of data transmission.

CONSTITUTION: A transmitting coil 11 constitutes a parallel resonance circuit together with a capacitor of a frequency modulating circuit 10. This circuit constitutes a positive feedback loop in which an output of an amplifier 20, a first receiving coil 21, the transmitting coil 11, a second receiving coil 22, and an input of the amplifier 20 become consecutive paths. In such a state, an oscillation by a resonance oscillation of the parallel resonance circuit occurs therein. Transmitting data S1 subjected to frequency modulation by the frequency modulating circuit 10 is demodulated by a frequency demodulating circuit 23 and outputted as receiving data S2.