In type 2 diabetic patients, tight blood glucose control often requires both fasting and post-prandial glucose control separately. In the diabetic patients already on the insulin glargine treatment for the control of fasting blood glucose, additional measures for the control of post-prandial glucose level are often required. Nateglinide and acarbose are frequently used for this purpose. We hypothesized that the short acting sulfonylurea "nateglinide" may be more efficacious in diabetic patients with appreciable endogenous insulin secretion, while acarbose may be more efficacious in patients with lower endogenous insulin secretion. And we also want to clarify the clinical and biochemical parameters that can predict the responsiveness to each agent in this multi-center randomized open cross-over clinical study.