In crevice corrosion of stainless steel, it is understood that cathodic reaction outside crevice supports the anodic reaction inside crevice. Aggressive water chemistry in a corroding crevice can only be sustained with a driving force. In general, O2 reduction at an external surface plays the major role to provide the driving force. On the other hand, cathodic reaction inside crevice, which is considered to be hydrogen generation, has been confirmed in recent years, but contribution of cathodic reaction inside crevice on propagation of crevice corrosion has not been quantitatively determined. In this study, propagation continuity of crevice corrosion without cathodic reaction outside crevice was investigated. Two types of specimen, 304L “full crevice specimen”, which has no free surface outside crevice, and 316L “outer cathode specimen” were used to observe cathodic reaction inside or outside crevice separately. The open circuit potential of the full crevice specimen was measured during the experiment. It showed that the corrosion continued to propagate by only the cathodic reaction inside crevice until the experiment was terminated. The coupling current measured with the outer cathode specimen was converted to volume of metal loss and was compared to the actual corrosion volume. It showed corrosion propagation due to the cathodic reaction inside the crevice at corrosion rate was about 10x smaller in average than the corrosion rate due to cathodic reactions outside the crevice. When oxygen is dissolved in water even at a few ppb, the reduction of oxygen entering a crevice can be a cathodic reaction in the crevice as well as hydrogen generation.