A wireless power-supplying system comprising: a power-transmitting device that includes: a voltage converter configured to convert a voltage; and an inverter circuit configured to convert power input from the voltage converter into alternating current power, wherein the power-transmitting device is configured to generate a magnetic field on the basis of the alternating current power output from the inverter circuit, and a power-receiving device configured to rectify power which is received by a receiving-side pad via the magnetic field and to smooth the rectified power using a filter circuit, wherein the power-transmitting device comprises: a communication unit configured to communicate with the power-receiving device; and a control unit, wherein the communication unit is configured to receive, from the power-receiving device, information on the power received by the power-receiving device, and characterised in that the control unit is configured to cause the communication unit to transmit an instruction for changing at least one of inductance and capacitance of an element which is disposed between the receiving-side pad and the filter circuit, or at the receiving-side pad or at the filter circuit, in the power-receiving device so as to decrease an impedance when the power-receiving side is viewed from an output terminal of the voltage converter so as to satisfy a condition that the received power approaches a target value when a voltage across an element of the voltage converter or the inverter circuit has reached an upper limit of a withstanding voltage of the element and it is determined that the received power of the power-receiving device has not reached a target value on the basis of the information. a power-transmitting device that includes: a voltage converter configured to convert a voltage; and an inverter circuit configured to convert power input from the voltage converter into alternating current power, wherein the power-transmitting device is configured to generate a magnetic field on the basis of the alternating current power output from the inverter circuit, and a voltage converter configured to convert a voltage; and an inverter circuit configured to convert power input from the voltage converter into alternating current power, wherein the power-transmitting device is configured to generate a magnetic field on the basis of the alternating current power output from the inverter circuit, and a power-receiving device configured to rectify power which is received by a receiving-side pad via the magnetic field and to smooth the rectified power using a filter circuit, wherein the power-transmitting device comprises: a communication unit configured to communicate with the power-receiving device; and a control unit, wherein the communication unit is configured to receive, from the power-receiving device, information on the power received by the power-receiving device, and characterised in that the control unit is configured to cause the communication unit to transmit an instruction for changing at least one of inductance and capacitance of an element which is disposed between the receiving-side pad and the filter circuit, or at the receiving-side pad or at the filter circuit, in the power-receiving device so as to decrease an impedance when the power-receiving side is viewed from an output terminal of the voltage converter so as to satisfy a condition that the received power approaches a target value when a voltage across an element of the voltage converter or the inverter circuit has reached an upper limit of a withstanding voltage of the element and it is determined that the received power of the power-receiving device has not reached a target value on the basis of the information. a communication unit configured to communicate with the power-receiving device; and a control unit, wherein the communication unit is configured to receive, from the power-receiving device, information on the power received by the power-receiving device, and characterised in that the control unit is configured to cause the communication unit to transmit an instruction for changing at least one of inductance and capacitance of an element which is disposed between the receiving-side pad and the filter circuit, or at the receiving-side pad or at the filter circuit, in the power-receiving device so as to decrease an impedance when the power-receiving side is viewed from an output terminal of the voltage converter so as to satisfy a condition that the received power approaches a target value when a voltage across an element of the voltage converter or the inverter circuit has reached an upper limit of a withstanding voltage of the element and it is determined that the received power of the power-receiving device has not reached a target value on the basis of the information.