The present specification discloses as one embodiment a power receiver for transmitting a message by using a power transmission signal. The power receiver comprises: a power reception portion for receiving the wireless power signal that is formed by a power transmitter; a demodulation portion for demodulating the received wireless power signal; a modulation portion for modulating the received wireless power signal; and a control portion for decoding a first packet from the wireless power signal that is demodulated by means of the demodulation portion, for determining whether a second packet that does not collide with the first packet which has been decoded can be transmitted, and for modulating the received wireless power signal so as to comprise the second packet by controlling the modulation portion, when transmission is possible according to the result of the determination.