PROBLEM TO BE SOLVED: To provide a diabetes improving agent or a composition each containing, as an active ingredient, a Laminaria japonica fermentation product which is obtained by fermenting Laminaria japonica by Bacillus natto, Laminaria japonica and Bacillus natto being traditionally eaten and safe.SOLUTION: There are provided: functional food, food materials and pet food each for preventing or improving diabetes, and each including, as an active ingredient, a Laminaria japonica fermentation product obtained by using Bacillus natto and, as internal agents, compositions for pharmaceuticals (including pharmaceuticals for animals), compositions for food and drink and compositions for feeding stuff, to be given to humans or non-human animals.
