In this non-contact power feeding system that is capable of transmitting power from a power transmitting device (1) to a power receiving device (2) by a magnetic field resonance scheme, the power transmitting device (1) is provided with first to n-th resonant circuits (TT[1]-TT[n]) which are provided with coils (TL) that are different in size, respectively, and which have a resonant frequency set to a prescribed reference frequency. Prior to power transmission, test magnetic fields are generated in sequence in the first to n-th resonant circuits to detect the amplitude of current flowing through the coils of respective resonant circuits, and the presence/absence of a foreign object is determined on the basis of the obtained first to n-th amplitude detected values, to control execution of the power transmission.