Provided is a sensor in which a current sensor that detects a current of a power line as a change in a magnetic field and a voltage sensor that detects a voltage of the power line using capacitive coupling are integrally formed. The transmission of signals related to substantially the same sections is omitted in order to effectively compress an output signal from the sensor and an output signal from the voltage sensor. When the amplitude and phase of a fundamental wave which are estimated from the output signal from the sensor and the amplitude and phase of harmonics are encoded, the amplitude and phase of the harmonics are relativized with a value for the fundamental wave.