A wireless power transfer system-charger comprising: a power supply; a transformer unit for converting a voltage supplied by the power supply into a direct current voltage; and a controller for adjusting a level of the DC voltage of the transformer unit, whereby the transformer unit includes: a DC-DC converter; and a divider for dividing an output voltage (Vout) of the DC-DC converter; characterized in that the transformer unit further includes: a control unit for controlling an error (Vc) of the output voltage (Vout) of the DC-DC converter based on a divided voltage (Vd), wherein the controller is connected to the divider to adjust a target value of the output voltage (Vout) of the DC-DC converter according to a wireless charging state, wherein the divider includes a plurality of resistors (R1, R2, R3) for dividing the output voltage (Vout) of the DC-DC converter and supplying the divided voltage (Vd) to the error amplifier, wherein the controller includes an output control port as an output terminal connected to the divider for adjusting the divided voltage (Vd). a power supply; a transformer unit for converting a voltage supplied by the power supply into a direct current voltage; and a controller for adjusting a level of the DC voltage of the transformer unit, whereby the transformer unit includes: a DC-DC converter; and a divider for dividing an output voltage (Vout) of the DC-DC converter; characterized in that the transformer unit further includes: a control unit for controlling an error (Vc) of the output voltage (Vout) of the DC-DC converter based on a divided voltage (Vd), wherein the controller is connected to the divider to adjust a target value of the output voltage (Vout) of the DC-DC converter according to a wireless charging state, wherein the divider includes a plurality of resistors (R1, R2, R3) for dividing the output voltage (Vout) of the DC-DC converter and supplying the divided voltage (Vd) to the error amplifier, wherein the controller includes an output control port as an output terminal connected to the divider for adjusting the divided voltage (Vd). a DC-DC converter; and a divider for dividing an output voltage (Vout) of the DC-DC converter; characterized in that the transformer unit further includes: a control unit for controlling an error (Vc) of the output voltage (Vout) of the DC-DC converter based on a divided voltage (Vd), wherein the controller is connected to the divider to adjust a target value of the output voltage (Vout) of the DC-DC converter according to a wireless charging state, wherein the divider includes a plurality of resistors (R1, R2, R3) for dividing the output voltage (Vout) of the DC-DC converter and supplying the divided voltage (Vd) to the error amplifier, wherein the controller includes an output control port as an output terminal connected to the divider for adjusting the divided voltage (Vd). a control unit for controlling an error (Vc) of the output voltage (Vout) of the DC-DC converter based on a divided voltage (Vd), wherein the controller is connected to the divider to adjust a target value of the output voltage (Vout) of the DC-DC converter according to a wireless charging state, wherein the divider includes a plurality of resistors (R1, R2, R3) for dividing the output voltage (Vout) of the DC-DC converter and supplying the divided voltage (Vd) to the error amplifier, wherein the controller includes an output control port as an output terminal connected to the divider for adjusting the divided voltage (Vd).