The present invention relates to an apparatus and a method for performing communication in a wireless power transmission system. The present specification discloses a wireless power transmission apparatus comprising: a communication/control unit configured to perform negotiation on a first available power index with a wireless power reception apparatus; and a power conversion unit configured to create magnetic coupling of a primary coil according to the first available power index, and transmit power wirelessly to the wireless power reception apparatus. The wireless power transmission apparatus can properly adjust an available power index in a dynamic manner at a time point desired by itself according to a surrounding environment/situation, and leadingly initiate communication and authentication.