An amplitude normalization circuit includes: a peak detector that detects a peak value of a full-wave rectified voltage of an AC voltage; a triangular wave oscillator connected to the peak detector generates a triangular wave voltage having the peak value; a comparator connected to the triangular oscillator compares the triangular wave voltage with the full-wave rectified voltage and outputs a pulse width modulation signal; and a waveform converter connected to the comparator converts a waveform of the pulse width modulation signal and outputs an output voltage with constant amplitude.