The present invention provides Lactobacillus bacteria which enhance the functional of Peyer's patch and promote IgA production and which have a characteristics of localizing on human intestine as well as an agent for promoting IgA production. The present invention is directed to an agent for promoting IgA production containing Lactobacillus amylovorus cells, especially Lactobacillus amylovorus CP1750 (FERM BP-10532) as an active ingredient.