Power receiving device, power transmitting device, wireless power transfer system, and wireless power transfer method

A power receiving unit includes a communication unit, a control unit, a detecting unit that performs metallic foreign matter detection, and a charge storage unit. The control unit is configured to control charging so electric power is stored in the charge storage unit for consumption by the detecting unit during Q-value measurement when the control unit receives a Q-value measurement command from the power transmitting device through the communication unit.