In this paper, totating bending fatigue tests are carried out in order to clarify the difference of initiation and growth behaviors of cracks in shot-peened carbon steel specimens and unpeened ones. The material used is an annealed S 45 C carbon steel. The difference between the two is clarified through the successive observations of the specimen surface by the replication technique and the measurement of the residual stress during the fatigue test. The effect of shot-peening on the growth behavior of a crack is discussed based on the fact that it is divided into three parts:the weakening effect in the damaged layer near the surface, the strengthening effect in the work-hardened layer with residual stress and the zero effect in the non-work-hardened zone.