To provide a non-contact power transfer system where voltage of DC power which is transferred to be constant in a non-contact manner, and to provide a power transmission device and an electric power receiving device.

The non-contact power transfer system is provided with the power transmission device 1 which transmits power without contact by supplying AC power to a transmission coil 13; and an electric power receiving device 2 having a receiving coil 21 which is magnetically coupled to the transmission coil 13, and a rectifier circuit 22 rectifying AC power which is electromagnetically induced to the receiving coil 21. The electric power receiving device 2 is provided with a voltage detecting circuit 26 detecting a voltage of DC power which the rectifier circuit 22 rectifies; a feedback circuit 27 generating a feedback signal based on a detection result of the voltage detecting circuit 26, and supplying it to the receiving coil 21. The power transmission device 1 has a control circuit increasing and decreasing AC power supplied to the transmission coil 13, in accordance with the feedback signal which is electromagnetically induced to the transmission coil 13.

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