A noncontact electric power feeding apparatus, comprising: a resonance element for supplying an alternative current electric power in a noncontact style in accordance with a resonance; an alternative current power source portion configured to generate an alternative current electric power to be supplied to said resonance element; and an automatic matching box provided between said alternative current power source portion and said resonance element, characzerised by said automatic matching box being composed of a directional coupler, an Analog/Digital (A/D) conversion circuit, a microcomputer, and an LC variable circuit, wherein: said directional coupler is a device of three ports that is configured to detect a reflected electric power which is changed in accordance with a coupling coefficient (k) between said noncontact electric power feeding apparatus and an electric power feeding destination, and to supply the reflected electric power thus detected to the A/D conversion circuit, said A/D conversion circuit is configured to convert the reflected electric power supplied thereto from the directional coupler into a digital signal and to supply the resulting digital signal to the microcomputer, which is configured to produce a control signal in accordance with which the LC variable circuit is controlled based on the magnitude of the reflected electric power from the A/D conversion circuit, and to supply the control signal thus produced to the LC variable circuit, and said LC variable circuit includes a variable inductor and a variable capacitor and is configured to control the variable inductor and the variable capacitor in accordance with the control signal supplied thereto from the microcomputer so as to reduce the magnitude of the reflected electric power to zero. a resonance element for supplying an alternative current electric power in a noncontact style in accordance with a resonance; an alternative current power source portion configured to generate an alternative current electric power to be supplied to said resonance element; and an automatic matching box provided between said alternative current power source portion and said resonance element, characzerised by said automatic matching said directional coupler is a device of three ports that is configured to detect a reflected electric power which is changed in accordance with a coupling coefficient (k) between said noncontact electric power feeding apparatus and an electric power feeding destination, and to supply the reflected electric power thus detected to the A/D conversion circuit, said A/D conversion circuit is configured to convert the reflected electric power supplied thereto from the directional coupler into a digital signal and to supply the resulting digital signal to the microcomputer, which is configured to produce a control signal in accordance with which the LC variable circuit is controlled based on the magnitude of the reflected electric power from the A/D conversion circuit, and to supply the control signal thus produced to the LC variable circuit, and said LC variable circuit includes a variable inductor and a variable capacitor and is configured to control the variable inductor and the variable capacitor in accordance with the control signal supplied thereto from the microcomputer so as to reduce the magnitude of the reflected electric power to zero.