The present invention provides a composition (a blood glucose increase inhibitor) that has an effect of lowering blood glucose level in a hyperglycemic patient and that is therefore used to reduce blood glucose level in the patient. The present invention further provides a composition that is used to prevent or treat diseases caused by hyperglycemia, in particular, diabetes and diabetic complications (a composition for preventing or treating diseases caused by hyperglycemia, an antidiabetic), based on the above-mentioned effect. A feature of the present invention is using a peptide consisting of the amino acid sequence of Leu-Ser-Glu-Leu as an active ingredient.
