The dependence of passive current noise on passivation potential and Passivation time was investigated for SUS 304 in 0.05M H
2SO
4 and in ethanol solutions of different H
2O concentration. The effect of Cl
- addition was also examined for H
2SO
4. It was found that the power spectral density (PSD) resulted from FFT analysis of the current noise depended on the passivation potential and the passivation time in H
2SO
4 solution in the absence of Cl
-, with respect to the PSD level and its changing mode. Moreover, the PSD level was confirmed to change markedly corresponding to a little change of H
2O concentration in the ethanol solution even in the passivation under a constant potential. From the above facts along with the effect of Cl
- addition on the PSD, the PSD level and its changing mode were interpreted in terms of the nature of two kinds of bound water incorporated in the passive film.
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