A power transmission system (100, 200) comprising: a power transmitting device configured to convert supplied AC or DC power into AC power and transmit the converted AC power via a transmission path; and a power receiving device configured to receive the AC power via the transmission path, wherein the power receiving device comprises: a rectifier configured to rectify the AC power received via the transmission path to DC power; a DC converter configured to perform DC conversion on the DC power output from the rectifier; and a power-receiving side control device configured to calculate, based on an input voltage of the DC converter, a current command value making input impedance of the DC converter equal to a preset value and to control the DC converter so that an input current of the DC converter equals the current command value; characterized in that the power transmitting device comprises: an AC converter configured to convert the supplied AC or DC power into the AC power; and a power-transmitting side control device configured to control a gain of the AC power in the AC converter; the power-receiving side control device is configured to transmit the current command value to the power-transmitting side control device; and the power-transmitting side control device is configured to control the gain of the AC power in the AC converter based on the current command value received from the power-receiving side control device so that input power of the DC converter is constant. a power transmitting device configured to convert supplied AC or DC power into AC power and transmit the converted AC power via a transmission path; and a power receiving device configured to receive the AC power via the transmission path, wherein the power receiving device comprises: a rectifier configured to rectify the AC power received via the transmission path to DC power; a DC converter configured to perform DC conversion on the DC power output from the rectifier; and a power receiving device configured to receive the AC power via the transmission path, wherein the power receiving device comprises: a rectifier configured to rectify the AC power received via the transmission path to DC power; a DC converter configured to perform DC conversion on the DC power output from the rectifier; and a rectifier configured to rectify the AC power received via the transmission path to DC power; a DC converter configured to perform DC conversion on the DC power output from the rectifier; and a power-receiving side control device configured to calculate, based on an input voltage of the DC converter, a current command value making input impedance of the DC converter equal to a preset value and to control the DC converter so that an input current of the DC converter equals the current command value; characterized in that the power transmitting device comprises: an AC converter configured to convert the supplied AC or DC power into the AC power; and a power-transmitting side control device configured to control a gain of the AC power in the AC converter; the power-receiving side control device is configured to transmit the current command value to the power-transmitting side control device; and the power-transmitting side control device is configured to control the gain of the AC power in the AC converter based on the current command value received from the power-receiving side control device so that input power of the DC converter is constant. an AC converter configured to convert the supplied AC or DC power into the AC power; and a power-transmitting side control device configured to control a gain of the AC power in the AC converter; the power-receiving side control device is configured to transmit the current command value to the power-transmitting side control device; and the power-transmitting side control device is configured to control the gain of the AC power in the AC converter based on the current command value received from the power-receiving side control device so that input power of the DC converter is constant.