Amplitude modulation circuit and non-contact power feeding device

An amplitude modulation circuit includes a resonance circuit powered by an oscillator (1) and comprising a power transmission coil (L1) with a first coil portion (L11), a second coil portion (L12), a modulation coil (L2), and a resonance condenser (C1); and a switch configured to switch between a state where the first coil portion and the second coil portion are connected in series and a state where the first coil portion (L11) and the modulation coil (L2) are connected in series according to a level switching timing of transmission data and a timing when a coil current in the resonance circuit becomes zero. The combined inductance of the first coil portion(L11) and the second coil portion (L12) connected in series and a combined inductance of the first coil portion (L11) and the modulation coil (L2) connected in series are equal.