A non-contact power supply device, comprising: - a primary winding; and - a secondary winding adapted to receive electric power from an alternating current power supply via the primary winding, wherein: - an impedance characteristic of Z1 with respect to a frequency is such that an extremum is provided in the proximity of a frequency (f 0) of a fundamental wave component of the alternating current power supply and - another impedance characteristic of Z2 with respect to the frequency is such that the frequency (f 0) of the fundamental wave component is provided between another frequency (f 2) which is nearest to the frequency (f 0) of the fundamental wave component and at which a minimal value is provided and still another frequency (f 3) which is nearest to the frequency of the fundamental wave component and at which a maximal value is provided, - Z1 denotes the impedance of only a primary side viewed from an output side of the alternating current power supply, with a coupling coefficient (κ) between the primary winding and the secondary winding zero value, - Z2 denotes the impedance of only a secondary side viewed from a load side connected to the secondary winding, with the coupling coefficient (κ) between the primary winding and the secondary winding zero value, characterized in that - the impedance characteristic of Z1 with respect to the frequency is such that a minimal value is provided as said extremum in the proximity of the frequency (f 0) of the fundamental wave component of the alternating current power supply and - the frequency (f 2) of Z2 at which the minimal value is provided is set within a half-value width (Δf) of the frequency (f 1) of Z1 at which the minimal value is provided. - a primary winding; and - a secondary winding adapted to receive electric power from an alternating current power supply via the primary winding, - an impedance characteristic of Z1 with respect to a frequency is such that an extremum is provided in the proximity of a frequency (f 0) of a fundamental wave component of the alternating current power supply and - another impedance characteristic of Z2 with respect to the frequency is such that the frequency (f 0) of the fundamental wave component is provided between another frequency (f 2) which is nearest to the frequency (f 0) of the fundamental wave component and at which a minimal value is provided and still another frequency (f 3) which is nearest to the frequency of the fundamental wave component and at which a maximal value is provided, - Z1 denotes the impedance of only a primary side viewed from an output side of the alternating current power supply, with a coupling coefficient (κ) between the primary winding and the secondary winding zero value, - Z2 denotes the impedance of only a secondary side viewed from a load side connected to the secondary winding, with the coupling coefficient (κ) between the primary winding and the secondary winding zero value, - the impedance characteristic of Z1 with respect to the frequency is such that a minimal value is provided as said extremum in the proximity of the frequency (f 0) of the fundamental wave component of the alternating current power supply and - the frequency (f 2) of Z2 at which the minimal value is provided is set within a half-value width (Δf) of the frequency (f 1) of Z1 at which the minimal value is provided.