A surface characteristics evaluation method of evaluating a residual stress in a subject made of a steel material subjected to a surface modification treatment, comprising: a preparation step of preparing a surface characteristics evaluation apparatus that includes an oscillator including an AC power supply and a frequency changing circuit , a detector including a coil and connected to the oscillator , and a measuring instrument connected to the frequency changing circuit and the detector ; a subject placement step of placing the subject in such a manner that an alternating magnetic field induced by the coil permeates into the subject; an eddy current generation step of generating an eddy current in the subject by activating the AC power supply to make the coil induce the alternating magnetic field and allowing the alternating magnetic field to permeate into the subject; a frequency change step of successively changing the frequency of the alternating current by the frequency changing circuit , thereby successively changing a depth of permeation of the alternating magnetic field into the subject; an impedance calculation step of calculating an impedance Z 1 for each of different frequencies by detecting a potential difference between opposite ends of the coil and a value of a current flowing through the coil; a reference impedance measurement step of preliminary measuring a reference impedance Z 0 at each of different frequencies for a subject yet to be subjected to the surface modification treatment; and an evaluation step in which impedance ratios between the reference impedance Z 0 and the impedance Z 1 are computed for each of the different frequencies, and the residual stress in the subject subjected to the surface modification treatment is evaluated based on the impedance ratios. a preparation step of preparing a surface characteristics evaluation apparatus that includes an oscillator including an AC power supply and a frequency changing circuit , a detector including a coil and connected to the oscillator , and a measuring instrument connected to the frequency changing circuit and the detector ; a subject placement step of placing the subject in such a manner that an alternating magnetic field induced by the coil permeates into the subject; an eddy current generation step of generating an eddy current in the subject by activating the AC power supply to make the coil induce the alternating magnetic field and allowing the alternating magnetic field to permeate into the subject; a frequency change step of successively changing the frequency of the alternating current by the frequency changing circuit , thereby successively changing a depth of permeation of the alternating magnetic field into the subject; an impedance calculation step of calculating an impedance Z 1 for each of different frequencies by detecting a potential difference between opposite ends of the coil and a value of a current flowing through the coil; a reference impedance measurement step of preliminary measuring a reference impedance Z 0 at each of different frequencies for a subject yet to be subjected to the surface modification treatment; and an evaluation step in which impedance ratios between the reference impedance Z 0 and the impedance Z 1 are computed for each of the different frequencies, and the residual stress in the subject subjected to the surface modification treatment is evaluated based on the impedance ratios. <EOS>