A terminal device comprising: a secondary-side coil configured to receive electric power transmitted from a primary-side coil of an electric power feeding device; a rectifier unit configured to rectify reception electric power obtained by the secondary-side coil; a control unit; a secondary-side communication unit configured to communicate with the electric power feeding device, the secondary-side communication unit being configured to transmit a load electric power level to the electric power feeding device, to receive a signal which confirms the load electric power level received by the electric power feeding device, to return the information indicating the load electric power level and to receive a confirmation signal of the load electric power level from the electric power feeding device, the secondary-side communication unit being further configured to receive information from the electric power feeding device, the information comprising information of a level of transmission electric power selected by the electric power feeding device on the basis of the confirmed load electric power level; the terminal device further comprising a regulator including a switching regulator and a series regulator, the regulator being configured to convert the reception electric power rectified by the rectifier unit to electric power of a predetermined voltage, and to conduct conversion by a first conversion method of the switching regulator or by a second conversion method of the series regulator controlled by the control unit,, the control unit being configured to determine whether the level of transmission electric power is larger than or equal to a threshold value on the basis of the information received by the secondary-side communication unit and to instruct to use the switching regulator if the transmission electric power level is larger than or equal to the threshold value and to use the series regulator if the transmission electric power level is smaller than the threshold value. a secondary-side coil configured to receive electric power transmitted from a primary-side coil of an electric power feeding device; a rectifier unit configured to rectify reception electric power obtained by the secondary-side coil; a control unit; a secondary-side communication unit configured to communicate with the electric power feeding device, the secondary-side communication unit being configured to transmit a load electric power level to the electric power feeding device, to receive a signal which confirms the load electric power level received by the electric power feeding device, to return the information indicating the load electric power level and to receive a confirmation signal of the load electric power level from the electric power feeding device, the secondary-side communication unit being further configured to receive information from the electric power feeding device, the information comprising information of a level of transmission electric power selected by the electric power feeding device on the basis of the confirmed load electric power level; the terminal device further comprising a regulator including a switching regulator and a series regulator, the regulator being configured to convert the reception electric power rectified by the rectifier unit to electric power of a predetermined voltage, and to conduct conversion by a first conversion method of the switching regulator or by a second conversion method of the series regulator controlled by the control unit,, the control unit being configured to determine whether the level of transmission electric power is larger than or equal to a threshold value on the basis of the information received by the secondary-side communication unit and to instruct to use the switching regulator if the transmission electric power level is larger than or equal to the threshold value and to use the series regulator if the transmission electric power level is smaller than the threshold value.