Provided s a non-contact power transmission system with which it is possible to individually detect the position of a receiving unit with respect to a transmission unit, even if there are positions at which the same microvoltage values are indicated, even if the distance differs, due to the shape of the transmission coil of the transmission unit and the receiving coil of the receiving unit. At a position at which the position differential value of the detected microvoltage exceeds a zero value, said positions set to the initial position (+xint) of the movement displacement of the vehicle, and the movement displacement on the basis of vehicle velocity is calculated to a position (+xc) at which the microvoltage value characteristics can be used from said initial position to (+xc to 0).