A composition of a peptide/β-1,3-glucan complex and an immunostimulatory polynucleotide, or a derivative thereof, wherein: said immunostimulatory polynucleotide, or derivative thereof, has a partial base sequence having immunostimulatory activity, and said peptide/β-1,3-glucan comprises: a polysaccharide having a β-1,3-glucan backbone; and a peptide/polynucleotide conjugate in which an antigenic peptide is bonded covalently to a polynucleotide or a derivative thereof, wherein: said polynucleotide of the peptide/polynucleotide conjugate has the base sequence of any one of polyriboadenylic acid (polyA), polyribocytidylic acid (polyC), polydeoxyadenylic acid (poly(dA)) and polydeoxythymidylic acid (poly(dT)); the derivative of said polynucleotide of the peptide/polynucleotide conjugate is said polynucleotide in which at least a portion of phosphodiester bonds of DNA or RNA is substituted by a phosphorothioate group; and said polynucleotide, or derivative thereof, of the peptide/polynucleotide conjugate bonds through hydrogen bonding with the polysaccharide having the β-1,3-glucan backbone, and forms a complex having a triple helix structure consisting of one molecular chain of the polynucleotide, or derivative thereof, and two molecular chains of the polysaccharide having the β-1,3-glucan backbone. said immunostimulatory polynucleotide, or derivative thereof, has a partial base sequence having immunostimulatory activity, and said peptide/β-1,3-glucan comprises: a polysaccharide having a β-1,3-glucan backbone; and a peptide/polynucleotide conjugate in which an antigenic peptide is bonded covalently to a polynucleotide or a derivative thereof, wherein: said polynucleotide of the peptide/polynucleotide conjugate has the base sequence of any one of polyriboadenylic acid (polyA), polyribocytidylic acid (polyC), polydeoxyadenylic acid (poly(dA)) and polydeoxythymidylic acid (poly(dT)); the derivative of said polynucleotide of the peptide/polynucleotide conjugate is said polynucleotide in which at least a portion of phosphodiester bonds of DNA or RNA is substituted by a phosphorothioate group; and said polynucleotide, or derivative thereof, of the peptide/polynucleotide conjugate bonds through hydrogen bonding with the polysaccharide having the β-1,3-glucan backbone, and forms a complex having a triple helix structure consisting of one molecular chain of the polynucleotide, or derivative thereof, and two molecular chains of the polysaccharide having the β-1,3-glucan backbone. a polysaccharide having a β-1,3-glucan backbone; and a peptide/polynucleotide conjugate in which an antigenic peptide is bonded covalently to a polynucleotide or a derivative thereof, wherein: said polynucleotide of the peptide/polynucleotide conjugate has the base sequence of any one of polyriboadenylic acid (polyA), polyribocytidylic acid (polyC), polydeoxyadenylic acid (poly(dA)) and polydeoxythymidylic acid (poly(dT)); the derivative of said polynucleotide of the peptide/polynucleotide conjugate is said polynucleotide in which at least a portion of phosphodiester bonds of DNA or RNA is substituted by a phosphorothioate group; and said polynucleotide, or derivative thereof, of the peptide/polynucleotide conjugate bonds through hydrogen bonding with the polysaccharide having the β-1,3-glucan backbone, and forms a complex having a triple helix structure consisting of one molecular chain of the polynucleotide, or derivative thereof, and two molecular chains of the polysaccharide having the β-1,3-glucan backbone. said polynucleotide of the peptide/polynucleotide conjugate has the base sequence of any one of polyriboadenylic acid (polyA), polyribocytidylic acid (polyC), polydeoxyadenylic acid (poly(dA)) and polydeoxythymidylic acid (poly(dT)); the derivative of said polynucleotide of the peptide/polynucleotide conjugate is said polynucleotide in which at least a portion of phosphodiester bonds of DNA or RNA is substituted by a phosphorothioate group; and said polynucleotide, or derivative thereof, of the peptide/polynucleotide conjugate bonds through hydrogen bonding with the polysaccharide having the β-1,3-glucan backbone, and forms a complex having a triple helix structure consisting of one molecular chain of the polynucleotide, or derivative thereof, and two molecular chains of the polysaccharide having the β-1,3-glucan backbone.