A survey shows that the most frequently observed direct cause of death in diabetic patients is cardiovascular disorder. However, investigations and surveys such as DCCT, UKPDS and KUMAMOTO-study, etc. clarified that strict control of blood sugar level prevented development and progress of diabetic microangiopathy, but could not show a significant effect on great vessel disorder. Recently, the DECODA-study, DECODE-study and Honolulu-study have demonstrated that postprandial high blood sugar is involved in great vessel disorder. Therefore, possible prevention of great vessel disorder in diabetic patients is suggested by improving the postprandial blood sugar level as achieved using ultrarapid-acting type insulin, which has become available recently. Even with results in Europe and the US obtained, the life-style and incidence of complications in Japanese people are different, and there are many points that remain uncertain with respect to the direct application of foreign results to Japanese people. Therefore, in Japan also, it is necessary to conduct a large-scale clinical study and to establish high-level evidence using mainly Japanese people through hospitals having many patients.