A contactless power transmission device comprising: an AC power supply adapted to output an AC power; a primary coil to which the AC power is inputted; a secondary coil adapted to reveive the AC power from the primary coil in a contactless manner; and a variable load that varies an impedance in accordance with an inputted power, wherein the AC power supply is configured to output a first AC power and a second AC power that differs in magnitude to each other as the AC power, wherein a power transmission line between the AC power supply and the variable load includes a first line and a second line different from the first line, and wherein the contactless power transmission device further comprises: a switching unit adapted to switch the power transmission line so that a first power is transmitted through the first line when the AC power supply outputs the first AC power and so that a second power is transmitted through the second line when the AC power supply outputs the second AC power; and an impedance conversion unit (31,50) arranged on the second line and adapted to convert an impedance from an output of the AC power supply to the variable load when the second power is transmitted through the second line to approach an impedance from the output of the AC power supply to the variable load when the first power is transmitted through the first line. an AC power supply adapted to output an AC power; a primary coil to which the AC power is inputted; a secondary coil adapted to reveive the AC power from the primary coil in a contactless manner; and a variable load that varies an impedance in accordance with an inputted power, wherein the AC power supply is configured to output a first AC power and a second AC power that differs in magnitude to each other as the AC power, wherein a power transmission line between the AC power supply and the variable load includes a first line and a second line different from the first line, and wherein the contactless power transmission device further comprises: a switching unit adapted to switch the power transmission line so that a first power is transmitted through the first line when the AC power supply outputs the first AC power and so that a second power is transmitted through the second line when the AC power supply outputs the second AC power; and an impedance conversion unit (31,50) arranged on the second line and adapted to convert an impedance from an output of the AC power supply to the variable load when the second power is transmitted through the second line to approach an impedance from the output of the AC power supply to the variable load when the first power is transmitted through the first line. a switching unit adapted to switch the power transmission line so that a first power is transmitted through the first line when the AC power supply outputs the first AC power and so that a second power is transmitted through the second line when the AC power supply outputs the second AC power; and an impedance conversion unit (31,50) arranged on the second line and adapted to convert an impedance from an output of the AC power supply to the variable load when the second power is transmitted through the second line to approach an impedance from the output of the AC power supply to the variable load when the first power is transmitted through the first line.