To provide a wireless power transmission system and a wireless power transmission method, capable of transmitting power in a mode of efficiently using a power of a communication master when operating a communication terminal with a wireless power transmitted from the communication master as a power source.

A vehicle 1 and an electronic key 2 are equipped with a wireless power transmission system 26 for causing the vehicle 1 to transmit a power radio wave Svv and operating the electronic key 2 by using the power radio wave Svv as a power source. Assuming that the electronic key 2 executes a reception operation with a small energy and requires a large energy for a transmission operation, the electronic radio wave Svv is transmitted at a low output in outward communication to allow the electronic key 2 to perform the transmission operation and the power radio wave Svv is transmitted at a high output in return communication to allow the electronic key 2 to perform the reception operation.

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