A purpose of the invention is to provide a novel IgA secretion promoter useful as a mucosal immunity stimulation agent. A significant action of promoting IgA secretion was observed in oral administration of indigestible dextrin.本發明的目的是提供一種有效用作黏膜免疫活化劑的新穎IgA分泌促進劑。藉由口服難消化性糊精而發現顯著的IgA分泌促進作用。