There is provided a single preparation which directly decreases both of the post prandial blood glucose level and the fasting blood glucose level close to normal levels, by release-sustaining a drug capable of decreasing the post prandial blood glucose level of diabetic patients close to the normal level, or mixing a controlled release drug capable of decreasing the post prandial blood glucose level close to the normal level with an immediate release drug. It is particularly preferable that the drug capable of decreasing the post prandial blood glucose level close to the normal level is nateglinide.