Power receiving device, power receiving method, and contactless power transmission system

The invention relates to a power receiving device, a power receiving method, and a contactless power transmission system. The power receiving device includes: a resonance circuit, which is configured to receive power sending signals and which includes a coil configured to be an outer coil electromagnetically coupled to a power sending device; a memory, which is configured to store a reference Q factor value; a control part, which is configured to obtain the reference Q factor value from the memory; and a charging part, which is configured to charge power obtained from the power sending signals and to supply power to the control part.