A speed detecting device, comprising: three neighboring excitation coils adapted to generate magnetic fluxes corresponding to alternating current (i inj) and having a central excitation coil and the other excitation coils at both sides of the central excitation coil, with the three excitation coils being disposed along a first direction, adapted to determine a moving speed of a conductive relative moving body movable along said first direction, and a winding direction of the central excitation coil being opposite to a winding direction of the other excitation coils; a current source, wherein the speed detecting device is arranged such that alternating current (i inj) is flowing from the current source to the central excitation coil, from the central excitation coil via the other excitation coils, which are connected electrically in parallel, and then back to the current source; a plurality of detection coils, each of the plurality of detection coils generating an induced voltage corresponding to magnetic flux produced by an eddy current generated on the conductive relative moving body, the eddy current being generated so as to correspond to the moving speed of the relative moving body moving through the magnetic fluxes generated by the alternating current (i inj) flowing through the three excitation coils; and a speed estimation portion for estimating, based on the induced voltage generated in each of the plurality of detection coils, the moving speed of the relative moving body, wherein the three excitation coils and the plurality of detection coils are disposed so that magnetic fluxes generated by the alternating current (i inj) flowing through the three excitation coils are linked with at least two of the plurality of detection coils, which are placed such that they experience the same magnetic flux when the relative moving body is stopped, but different magnetic fluxes when the relative moving body is moving, and wherein the speed detecting device is arranged such that the moving speed is determined from a difference between the induced voltages of the two detection coils. three neighboring excitation coils adapted to generate magnetic fluxes corresponding to alternating current (i inj) and having a central excitation coil and the other excitation coils at both sides of the central excitation coil, with the three excitation coils being disposed along a first direction, adapted to determine a moving speed of a conductive relative moving body movable along said first direction, and a winding direction of the central excitation coil being opposite to a winding direction of the other excitation coils; a current source, wherein the speed detecting device is arranged such that alternating current (i inj) is flowing from the current source to the central excitation coil, from the central excitation coil via the other excitation coils, which are connected electrically in parallel, and then back to the current source; a plurality of detection coils, each of the plurality of detection coils generating an induced voltage corresponding to magnetic flux produced by an eddy current generated on the conductive relative moving body, the eddy current being generated so as to correspond to the moving speed of the relative moving body moving through the magnetic fluxes generated by the alternating current (i inj) flowing through the three excitation coils; and a speed estimation portion for estimating, based on the induced voltage generated in each of the plurality of detection coils, the moving speed of the relative moving body, wherein the three excitation coils and the plurality of detection coils are disposed so that magnetic fluxes generated by the alternating current (i inj) flowing through the three excitation coils are linked with at least two of the plurality of detection coils, which are placed such that they experience the same magnetic flux when the relative moving body is stopped, but different magnetic fluxes when the relative moving body is moving, and wherein the speed detecting device is arranged such that the moving speed is determined from a difference between the induced voltages of the two detection coils.