An eddy current sensor that includes: a probe having an exciting portion for applying a predetermined alternating-current excitation signal to a measurement object component (6; C; W) and a detecting portion for detecting a detection signal generated in the measurement object component owing to the applied alternating-current excitation signal; and a computing unit for calculating the detection signal as a measured eddy current value, characterized in that the exciting portion includes a first excitation coil (51; 351; 451) that is arranged so that a center axis direction of the first excitation coil (51; 351; 451) is oriented in a first axis direction and a second excitation coil (52; 352; 452) that is arranged to intersect with the first excitation coil (51; 351; 451) so that a center axis direction of the second excitation coil (52; 352; 452) is oriented in a second axis direction perpendicular to the first axis direction, the detecting portion includes a first detection coil (61; 361; 461) that is arranged at one of two intersecting portions of the first excitation coil (51; 351; 451) and the second excitation coil (52; 352; 452), wherein the eddy current sensor further comprises means configured to apply an alternating-current voltage to each of the first excitation coil and the second excitation coil as the alternating-current excitation signal in a state where the probe is arranged in proximity to the measurement object component in position such that the detection coil faces a measured portion of the measurement object component, a first magnetic field in the first axis direction and a second magnetic field in the second axis direction are generated at a portion of the measurement object component, facing the detection coil, to generate eddy currents by the first and second magnetic fields, wherein the detection coil is configured to detect induced voltages generated by the eddy currents as the detection signal, the computing unit is configured to calculate the detection signal as a measured eddy current value to thereby measure a hardness penetration of the portion of the measurement object component, facing the detection coil, on the basis of the measured eddy current value, the detecting portion includes one or two quenching determination coils (162a, 162b) that are arranged adjacent to the detection coil on one side or both sides in the first axis direction, and wherein the means is configured to apply the alternating-current voltage to each of the first excitation coil and the second excitation coil as the alternating-current excitation signal in a state where the probe is arranged in proximity to the measurement object component in position such that the detection coil and each quenching determination coil (162a, 162b) face the measured portion of the measurement object component, a magnetic field in a direction perpendicular to the first axis direction and the second axis direction is generated at a portion of the measurement object component, facing each quenching determination coil (162a, 162b), to generate eddy current by the magnetic field, each quenching determination coil (162a, 162b) is configured to detect induced voltage generated by the eddy current as a detection signal, and the computing unit is configured to calculate the detection signal of each quenching determination coil (162a, 162b) as a measured eddy current value to thereby determine whether the portion of the measurement object component, facing each quenching determination coil, is quenched or not quenched on the basis of the measured eddy current value.