The present invention provides an agent for recovering insulin secretion function which contains at least one of the amino acids selected from the group consisting of aspartic acid, cystine, serine, asparagine, isoleucine, histidine, hydroxyproline, glutamic acid, valine and salts thereof as an active ingredient; a functional food which contains the agent for recovering insulin secretion function; and a composition for treating diabetes which contains the amino acid(s) and a second diabetic drug as active ingredients. This agent for recovering insulin secretion function can be used as an oral therapeutic agent or functional food that is useful for treating, improving or preventing insulin secretion defects in Type II diabetes, borderline diabetes and other diseases, and side effects caused by administration of drugs.