A contactless inductively coupled power transfer system includes a power supply device and a power receiving device. The power supply device includes a primary winding for generating an electromagnetic field (EMF) in response to an AC current flow having an operating frequency. The power receiving device includes a resonant circuit outputting an output voltage to a load and including a secondary winding and a reactance element. The reactance element is capable of forming a parallel resonant LC circuit with the secondary winding that resonates at the operating frequency, and forming a series resonant LC circuit that resonates at the operating frequency, and that is to be connected in series to the load.