A power transmission system comprising: a power transmitting device configured to convert supplied alternating current or direct current 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 transmitting device comprises: an AC converter (11a, 11b) configured to perform AC conversion on the supplied AC power or DC power; a power-transmitting side resonance coil configured to wirelessly transmit the AC power obtained from the AC converter (11a, 11b) under a magnetic field resonance method; and a power-transmitting side control device configured to control the AC converter (11a, 11b), wherein the power receiving device comprises: a power-receiving side resonance coil configured to wirelessly receive the AC power from the power-transmitting side resonance coil; a rectifier configured to convert the AC power received by the power-receiving side resonance coil into the 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 control the DC converter; characterized in that, the power receiving device further comprises a power-source circuit configured to generate a control power voltage from an output voltage of the rectifier and output the generated control power voltage to the power-receiving side control device, wherein the power-receiving side control device is configured to measure the output voltage of the rectifier after being activated by input of the control power voltage and to transmit a measurement result to the power-transmitting side control device, and wherein the power-transmitting side control device is configured to control the AC converter (11a, 11b) for a period from a transmission start time of the AC power to a time when the measurement result of the output voltage of the rectifier is received so that the output voltage of the rectifier is gradually raised without exceeding a value suitable as an input voltage of the DC converter, and, after receiving the measurement result, to control the AC converter (11a, 11b) based on the measurement result so that the output voltage of the rectifier becomes the suitable value. a power transmitting device configured to convert supplied alternating current or direct current 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 transmitting device comprises: an AC converter (11a, 11b) configured to perform AC conversion on the supplied AC power or DC power; a power-transmitting side resonance coil configured to wirelessly transmit the AC power obtained from the AC converter (11a, 11b) under a magnetic field resonance method; and a power-transmitting side control device configured to control the AC converter (11a, 11b), an AC converter (11a, 11b) configured to perform AC conversion on the supplied AC power or DC power; a power-transmitting side resonance coil configured to wirelessly transmit the AC power obtained from the AC converter (11a, 11b) under a magnetic field resonance method; and a power-transmitting side control device configured to control the AC converter (11a, 11b), wherein the power receiving device comprises: a power-receiving side resonance coil configured to wirelessly receive the AC power from the power-transmitting side resonance coil; a rectifier configured to convert the AC power received by the power-receiving side resonance coil into the 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 control the DC converter; characterized in that, the power receiving device further comprises a power-source circuit configured to generate a control power voltage from an output voltage of the rectifier and output the generated control power voltage to the power-receiving side control device, a power-receiving side resonance coil configured to wirelessly receive the AC power from the power-transmitting side resonance coil; a rectifier configured to convert the AC power received by the power-receiving side resonance coil into the 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 control the DC converter; characterized in that, the power receiving device further comprises a power-source circuit configured to generate a control power voltage from an output voltage of the rectifier and output the generated control power voltage to the power-receiving side control device, wherein the power-receiving side control device is configured to measure the output voltage of the rectifier after being activated by input of the control power voltage and to transmit a measurement result to the power-transmitting side control device, and wherein the power-transmitting side control device is configured to control the AC converter (11a, 11b) for a period from a transmission start time of the AC power to a time when the measurement result of the output voltage of the rectifier is received so that the output voltage of the rectifier is gradually raised without exceeding a value suitable as an input voltage of the DC converter, and, after receiving the measurement result, to control the AC converter (11a, 11b) based on the measurement result so that the output voltage of the rectifier becomes the suitable value.