It can be said that it also exists the relationship of Hall-Petch which it is possible to increase proof stress by decreasing a grain diameter about austenitic stainless steel SUS304. In order to make grain diameter of SUS304 small, it must make use of the recrystallization after it is done hot roll and cold roll since phase transformation does not happen in heating and cooling processes. On the other hand, in order to increase the fatigue strength of HIP device or automobile parts, authors were clear the process of fatigue fracture and defensive factors, and was proposed the new improvement method on fatigue strength. By decreasing grain diameter, it can be expected effects such as, (1) proof stress become high (2) it can obtain a greater compressive residual stress (3) it is possible to be short fatigue crack length of stage I. In this study, in order to investigate the relationship between grain diameter and fatigue strength, it was carried out experiment by using the metal bellows of SUS304,and grain diameter was adjusted by changing BA temperature after cold roll. It could be obtained the results that fatigue strength was improved in proportion with decreasing grain diameter.