A communication circuit is provided which transmits an information bit string from a transmission unit to a reception unit. The transmission unit includes a first modulation circuit that modulates a first carrier wave by a start bit to generate a first frequency signal, a second modulation circuit that modulates a second carrier wave by the information bit string to generate a second frequency signal, and a transmission circuit that transmits the first and second frequency signals from a transmitting antenna. The reception unit includes a reception circuit that receives a signal from the transmission unit, a first detector circuit that detects a signal of the first carrier wave to demodulate the start bit, a second detector circuit that detects a signal of the second carrier wave to demodulate the information bit string, and a detection circuit that is synchronized by the start bit and reads the information bit string.