A first circuit generates and outputs a transmission signal to a first end and a second end of a first coil in response to variation in logical value of an input first signal. A detection circuit detects a voltage signal generated at each of a first end and a second end and outputs a second signal which reflects the first signal based on a result of detection. A control circuit controls a voltage to be applied across opposing ends of each of a first diode and a second diode of a first rectifier circuit and a voltage to be applied to opposing ends of each of a third diode and a fourth diode of a second rectifier circuit.