A wireless power transmission system includes a power control device, a power transmitting device, a relay device, and a power receiving device. The power control device includes a direct-current power supply, and a main control circuit that generates a first load instruction value and a second load instruction value. The power transmitting device returns a first response signal and information on alternating-current power supplied to a load circuit in the relay device, such as a voltage value, when receiving the first load instruction value. The load circuit returns a second response signal when receiving the second load instruction value. The main control circuit determines that not the load circuit but the relay-side power receiving circuit is faulty when not receiving the second response signal within a first period and receiving the first response signal within a second period and not receiving is the information within a second period.