An object of the present invention is to provide an adjuvant for a mucosal vaccine with high safety that induces a sufficient immune response in a mucosal membrane. According to the present invention, an adjuvant for a mucosal vaccine containing a protein complex composed of hemagglutinin (HA) subcomponents HA1 and HA2, and mutant subcomponent HA3 of botulinum toxin is provided.
