A power receiving device and a power feeding system which are capable of performing communication and power feeding at the same time are provided. Further, a power receiving device and a power feeding system which are capable of stably performing communication during power feeding are provided. One embodiment of the present invention relates to a power receiving device which includes an antenna for communication and power feeding that receives AC power, a rectifier circuit that rectifies the received AC power including the modulation signal into DC power, a smoothing circuit that smoothes the resulting DC power, a power storage device that stores the smoothed DC power, a communication control unit that analyzes the modulation signal included in the AC power, and a transformer that is positioned between the antenna and the rectifier circuit and changes a reference potential of the AC power, and a power feeding device.