A nucleic acid molecule, comprising a nucleotide sequence encoding a polypeptide carrier, wherein, the polypeptide carrier is selected from: RBHBcAg carrier, which differs from RBHBcAg protein in that: (a) one or more amino acid residues, i.e. 1, 2, 3, 4, 5 or 6 amino acid residues, of the amino acid residues from positions corresponding to positions 78 to 83 of SEQ ID NO: 1 at N-terminus of RBHBcAg protein are deleted or substituted with a linker; and (b) 35 to 40 amino acid residues at C-terminus of RBHBcAg protein are deleted; and TBHBcAg carrier, which differs from TBHBcAg protein in that: (a) one or more amino acid residues, i.e. 1, 2, 3, 4 or 5 amino acid residues, of the amino acid residues from positions corresponding to positions 80 to 84 of SEQ ID NO: 2 at N-terminus of TBHBcAg protein are deleted or substituted with a linker; and (b) 30 to 35 amino acid residues at C-terminus of TBHBcAg protein are deleted; wherein the nucleic acid molecule further comprises a nucleotide sequence encoding a target polypeptide, wherein the target polypeptide is an epitope peptide comprising amino acids from positions 113 to 135 of HBsAg protein from human HBV, and said nucleotide sequence is inserted at a position of nucleotides encoding the one or more amino acid residues that are deleted as defined in (a), or (a), or is inserted in the nucleotide sequence encoding the linker or at either or both of the termini thereof; wherein said polypeptide carrier is able to present the target polypeptide; wherein the linker is a peptide linker; and wherein RBHBcAg is a core antigen protein from roundleaf bat hepatitis B virus, TBHBcAg is a core antigen protein from tent-making bat hepatitis B virus, and the HBsAg protein from human HBV is the surface antigen protein of human hepatitis B virus. RBHBcAg carrier, which differs from RBHBcAg protein in that: (a) one or more amino acid residues, i.e. 1, 2, 3, 4, 5 or 6 amino acid residues, of the amino acid residues from positions corresponding to positions 78 to 83 of SEQ ID NO: 1 at N-terminus of RBHBcAg protein are deleted or substituted with a linker; and (b) 35 to 40 amino acid residues at C-terminus of RBHBcAg protein are deleted; and TBHBcAg carrier, which differs from TBHBcAg protein in that: (a) one or more amino acid residues, i.e. 1, 2, 3, 4 or 5 amino acid residues, of the amino acid residues from positions corresponding to positions 80 to 84 of SEQ ID NO: 2 at N-terminus of TBHBcAg protein are deleted or substituted with a linker; and (b) 30 to 35 amino acid residues at C-terminus of TBHBcAg protein are deleted; wherein the nucleic acid molecule further comprises a nucleotide sequence encoding a target polypeptide, wherein the target polypeptide is an epitope peptide comprising amino acids from positions 113 to 135 of HBsAg protein from human HBV, and said nucleotide sequence is inserted at a position of nucleotides encoding the one or more amino acid residues that are deleted as defined in (a), or (a), or is inserted in the nucleotide sequence encoding the linker or at either or both of the termini thereof; wherein said polypeptide carrier is able to present the target polypeptide; wherein the linker is a peptide linker; and wherein RBHBcAg is a core antigen protein from roundleaf bat hepatitis B virus, TBHBcAg is a core antigen protein from tent-making bat hepatitis B virus, and the HBsAg protein from human HBV is the surface antigen protein of human hepatitis B virus. wherein the nucleic acid molecule further comprises a nucleotide sequence encoding a target polypeptide, wherein the target polypeptide is an epitope peptide comprising amino acids from positions 113 to 135 of HBsAg protein from human HBV, and said nucleotide sequence is inserted at a position of nucleotides encoding the one or more amino acid residues that are deleted as defined in (a), or (a), or is inserted in the nucleotide sequence encoding the linker or at either or both of the termini thereof; wherein said polypeptide carrier is able to present the target polypeptide; wherein the linker is a peptide linker; and wherein RBHBcAg is a core antigen protein from roundleaf bat hepatitis B virus, TBHBcAg is a core antigen protein from tent-making bat hepatitis B virus, and the HBsAg protein from human HBV is the surface antigen protein of human hepatitis B virus.