Non-contact power feeding system

In a normal mode, a power receiving device changes the resonant frequency of a power receiving side resonant circuit from a reference frequency or short-circuits a power receiving side coil for a predetermined time and then eliminates the changed or short-circuited state. Meanwhile, in the normal mode, a power transmitting device generates a test magnetic field in a power transmitting side coil during the above changed or short-circuited period and then determines, on the basis of a current amplitude detection value of the power transmitting side coil, whether a foreign object is present or not, thereby determining and controlling whether power transmission is executed or not. In a test mode, the power receiving device maintains the above changed or short-circuited state, and the power transmitting device continuously generates the test magnetic field and continuously obtains the current amplitude detection value of the power transmitting side coil.