A non-contact power supply apparatus, comprising: an inverter circuit which includes a plurality of conversion switching elements (Q1 to Q4) electrically connected between a pair of input points (211, 212) and a pair of output points (213, 214) and which is configured to convert a direct-current voltage applied to the pair of input points (211, 212) into an alternating-current voltage by switching the plurality of conversion switching elements (Q1 to Q4) and to output the alternating-current voltage from the pair of output points (213, 214); a primary coil electrically connected between the output points (213, 214) in the pair and configured to supply output power to a secondary coil in a non-contact manner when the alternating-current voltage is applied to the primary coil; a variable capacitance circuit electrically connected between the pair of output points (213, 214) and the primary coil, including an adjustment capacitor and a plurality of adjustment switching elements (Q5 to Q8), and configured to adjust a magnitude of a capacity component between the pair of output points (213, 214) and the primary coil by switching the plurality of adjustment switching elements (Q5 to Q8); and a control circuit configured to control the plurality of conversion switching elements (Q1 to Q4) by a first drive signal (G1 to G4) and to control the plurality of adjustment switching elements by a second drive signal (G5 to G8), characterized in that the control circuit is configured to adjust a phase difference which is a delay of a phase of the second drive signal (G6, G7) to a phase of the first drive signal (G1, G4) to a set value within a prescribed range to adjust a magnitude of the output power, wherein the prescribed range includes at least one of a range of 270 degrees to 360 degrees and a range of 90 degrees to 180 degrees. an inverter circuit which includes a plurality of conversion switching elements (Q1 to Q4) electrically connected between a pair of input points (211, 212) and a pair of output points (213, 214) and which is configured to convert a direct-current voltage applied to the pair of input points (211, 212) into an alternating-current voltage by switching the plurality of conversion switching elements (Q1 to Q4) and to output the alternating-current voltage from the pair of output points (213, 214); a primary coil electrically connected between the output points (213, 214) in the pair and configured to supply output power to a secondary coil in a non-contact manner when the alternating-current voltage is applied to the primary coil; a variable capacitance circuit electrically connected between the pair of output points (213, 214) and the primary coil, including an adjustment capacitor and a plurality of adjustment switching elements (Q5 to Q8), and configured to adjust a magnitude of a capacity component between the pair of output points (213, 214) and the primary coil by switching the plurality of adjustment switching elements (Q5 to Q8); and a control circuit configured to control the plurality of conversion switching elements (Q1 to Q4) by a first drive signal (G1 to G4) and to control the plurality of adjustment switching elements by a second drive signal (G5 to G8), characterized in that the control circuit is configured to adjust a phase difference which is a delay of a phase of the second drive signal (G6, G7) to a phase of the first drive signal (G1, G4) to a set value within a prescribed range to adjust a magnitude of the output power, wherein the prescribed range includes at least one of a range of 270 degrees to 360 degrees and a range of 90 degrees to 180 degrees.