We claim:
1. A method of presenting a cyclic peptide on a protein having a loop structure,
comprising:
using, as the cyclic peptide, that having a chemically crosslinked structure for forming an intramolecular cyclic structure, and
replacing the chemically crosslinked structure of the cyclic peptide with two amino acid residues constituting the loop structure and fusing the cyclic peptide to the protein having a loop structure.
2. The method according to Claim 1, wherein the two amino acid residues constituting the loop structure have a Ca atomic distance within a range of from 4 to ik.
3. The method according to Claim 1 or 2, wherein the protein having a loop structure has from 1 to 15 amino acid residues between the two amino acid residues constituting the loop structure.
4. The method according to any one of Claims 1 to 3, wherein the cyclic peptide is composed of a proteinogenic amino acid and/or a non-proteinogenic amino acid.
5. The method according to any one of Claims 1 to 4, wherein the chemically crosslinked structure contains a thioether bond or a disulfide bond.
6. The method according to any one of Claims 1 to 5, wherein two or more cyclic peptides each fuse to respectively different loop structures of a protein having a plurality of loop structures.
7. The method according to Claim 6, wherein the two or more cyclic peptides have the same amino acid sequence.

8. The method according to Claim 6, wherein the two or more cyclic peptides have respectively different amino acid sequences.
9. The method according to any one of Claims 1 to 8, wherein in replacing the chemically crosslinked structure of the cyclic peptide with the two amino acid residues constituting the loop structure, the chemically crosslinked structure of the cyclic peptide is replaced, via a linker sequence, with the two amino acid residues constituting the loop structure.
10. The method according to any one of Claims 1 to 9, wherein the chemically crosslinked structure of the cyclic peptide is replaced with the two amino acid residues constituting the loop structure while including an amino acid sequence constituting the loop structure other than the two amino acids constituting the loop structure.
11. A method of fusing a cyclic peptide to a protein having a loop structure, thereby producing a modified protein having the cyclic peptide presented on the protein, comprising:
using, as the cyclic peptide, that having a chemically crosslinked structure for forming an intramolecular cyclic structure,
selecting, from an amino acid sequence of the cyclic peptide, a partial amino acid sequence to be presented on the protein and selecting a base sequence corresponding to the partial amino acid sequence,
selecting base sequences corresponding to two amino acid sequences constituting the loop structure of the protein having a loop structure, respectively, removing a base present between the selected base sequences if necessary, and preparing a nucleic acid having, inserted and incorporated therein, the base

sequence corresponding to the partial amino acid sequence of the selected cyclic peptide, and
transiating the nucleic acid.
12. A modified protein obtained by the production method as claimed in Claim 11.