A power line signal encoder comprising: an estimation unit that estimates an amplitude and a phase of a fundamental wave and harmonics of a voltage waveform in a predetermined section; a relativization unit that relativizes information of the amplitude and the phase of the harmonics of the voltage waveform with information of the amplitude and the phase of the fundamental wave; and a quantization unit that quantizes each of the information of the amplitude and the phase of the fundamental wave and the harmonics with a predetermined number of bits; wherein the estimation unit estimates an amplitude and a phase of a fundamental wave and harmonics of a current waveform in a predetermined section, the relativization unit relativizes information of the amplitude and the phase of the harmonics of the current waveform with information of the amplitude and the phase of the fundamental wave of the current waveform, and the quantization unit quantizes each of the information of the amplitude and the phase of the fundamental wave and the harmonics of the current wave with the predetermined number of bits, characterized in that the relativization unit relativizes the amplitude on the basis of a ratio of the amplitude of the harmonics of the current waveform and the voltage waveform and the amplitude of the fundamental wave of the current waveform and the voltage waveform, and the relativization unit converts the phase of the harmonics of the current waveform and the voltage waveform into a phase when the phase of the fundamental wave of the current waveform and the voltage waveform is zero to relativize the phase of the harmonics. an estimation unit that estimates an amplitude and a phase of a fundamental wave and harmonics of a voltage waveform in a predetermined section; a relativization unit that relativizes information of the amplitude and the phase of the harmonics of the voltage waveform with information of the amplitude and the phase of the fundamental wave; and a quantization unit that quantizes each of the information of the amplitude and the phase of the fundamental wave and the harmonics with a predetermined number of bits; wherein the estimation unit estimates an amplitude and a phase of a fundamental wave and harmonics of a current waveform in a predetermined section, the relativization unit relativizes information of the amplitude and the phase of the harmonics of the current waveform with information of the amplitude and the phase of the fundamental wave of the current waveform, and the quantization unit quantizes each of the information of the amplitude and the phase of the fundamental wave and the harmonics of the current wave with the predetermined number of bits, characterized in that the relativization unit relativizes the amplitude on the basis of a ratio of the amplitude of the harmonics of the current waveform and the voltage waveform and the amplitude of the fundamental wave of the current waveform and the voltage waveform, and the relativization unit converts the phase of the harmonics of the current waveform and the voltage waveform into a phase when the phase of the fundamental wave of the current waveform and the voltage waveform is zero to relativize the phase of the harmonics.