Wireless power transfer system

A wireless power transfer system configured to wirelessly supply power from a power supplying device to a power receiving device, wherein

• the power supplying device includes:
• a power transmission circuit configured to transmit AC power, and
• a power transmission resonance circuit configured to include a power transmission coil,
• the power receiving device includes a power reception resonance circuit including a power reception coil, and
• at least one relay resonance circuit is arranged between the power transmission coil and the power reception coil,
• the relay resonance circuit includes at least one relay coil,
• in a state where a coupling coefficient between the coils included in two adjacent resonance circuits of the power transmission resonance circuit, the relay resonance circuit, and the power reception resonance circuit is a predetermined coupling coefficient, resonance of a first resonance mode and resonance of a second resonance mode are generated in the two adjacent resonance circuits, and the first resonance mode has a first resonance frequency and the second resonance mode has a second resonance frequency, the second resonance frequency being higher than the first resonance frequency,
• a resonance frequency of the two adjacent resonance circuits is set to a value which is one of the first resonance frequency and the second resonance frequency, and the set value is a frequency which deviates from a corresponding reference resonance frequency by a predetermined deviation frequency or more, and a resonance frequency of the resonance circuit other than the two adjacent resonance circuits is set to a reference resonance frequency, and
• a driving frequency of the AC power is set to the set value which is one of the first and second resonance frequencies and is set as the resonance frequency of the two adjacent resonance circuits.