A protein complex composed of hemagglutinin subcomponents HA1, HA2, and HA3 of botulinum toxin for the use as an adjuvant for a mucosal vaccine against diseases of the respiratory apparatus or the digestive apparatus, wherein the protein complex is administered to mucosa in combination with vaccine antigens from influenza viruses and wherein the protein complex is composed of the first component, the second component, and the third component described below: the first component: (a) a protein consisting of the amino acid sequence as shown in the following sequence (b) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (a); the second component: (c) a protein consisting of the amino acid sequence as shown in the following sequence (d) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (c); and the third component: (e) a protein consisting of the amino acid sequence as shown in the following sequence (f) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (e). the first component: (a) a protein consisting of the amino acid sequence as shown in the following sequence (b) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (a); (a) a protein consisting of the amino acid sequence as shown in the following sequence (b) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (a); the second component: (c) a protein consisting of the amino acid sequence as shown in the following sequence (d) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (c); and (c) a protein consisting of the amino acid sequence as shown in the following sequence (d) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (c); and the third component: (e) a protein consisting of the amino acid sequence as shown in the following sequence (f) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (e). (e) a protein consisting of the amino acid sequence as shown in the following sequence (f) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in the following sequence by deletion, substitution, or addition of one to 10 amino acids and having mucosal adjuvant activity that enhances production of antigen-specific antibody when the adjuvant is administered transmucosally in combination with vaccine antigens in both the mucosal and systemic immune response equivalent to those of the protein (e).