The present invention provides a Peyer's patch activator containing a polysaccharide obtained from sugar cane as an active ingredient, wherein the polysaccharide contains ±-glucan as a main component and has a peak molecular weight within a range of 720,000 to 1,080,000, with a proportion of glucose in all component sugars being 80% or more, and proportions of nonreducing terminal glucose and ±-1,6-linked glucose being 20 to 30% and 15 to 25%, respectively.