To provide a power transfer-type electronic key system which can operate an electronic key by using a received high-frequency radio wave as a power supply, and can be simply constituted, a method for supplying electric power to the electronic key, and the electronic key.

When a door handle knob outside a vehicle is touch-operated in the case that, for example, the power supply of the vehicle 1 is in an off-state, a car navigation system 27 puts a cellular phone T into a speaking state via a handsfree speaking system, and transmits a speaking radio wave Stp from the cellular phone T. The electronic key 2 receives the speaking radio wave Stp via an electric power collecting circuit 32, and performs various operations such as smart verification by using the speaking radio wave Stp as the power supply.

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