A peptide consisting of the sequence represented by H-X 1 -D-G-X 2 -F-X 3 -D-X 4 -Y-X 5 -R-Y-R-K-X 6 -X 7 -A-V-K-K-Y-L-A-A-V-L (SEQ ID NO: 3) {wherein X 1 is a neutral amino acid, X 2 is a neutral amino acid, X 3 is a neutral amino acid, X 4 is alanine, serine, Ai or Cn, X 5 is alanine, serine, Ai or Cn, X 6 is glutamine or alanine and X 7 is non-polar amino acid}, with the aspartic acids at position 3 and position 8 each independently replaced by a residue selected from the group consisting of tetrazole-substituted aspartic acid (Tz), tetrazole-substituted glutamic acid (egTz), tetrazole-substituted homoglutamic acid (nvTz), sulfoxy-substituted aspartic acid (cya) and oxadiazolone-substituted aspartic acid (SOxa), or its modified sequence, wherein the peptide has affinity for PAC1R and VPAC1R, and the modified sequence is the sequence listed as SEQ ID NO: 3, wherein: (A) 1 to 10 amino acids are added at the N-terminal end or C-terminal end, or (B) one sequence selected from the group consisting of the following: GKRYKQRVKNK (SEQ ID NO: 43); GKRYKQRVKN (SEQ ID NO: 44); GKRYKQRVK (SEQ ID NO: 45); GKRYKQRV (SEQ ID NO: 46); GKRYKQR (SEQ ID NO: 47); GKRYKQ (SEQ ID NO: 48); GKRYK (SEQ ID NO: 49); GKRY (SEQ ID NO: 50) GKR; GRR; GK; and GR G; is added to the C-terminus of the peptide, or (C) one or two, preferably one amino acid is deleted at the N-terminal or C-terminal end. X 1 is a neutral amino acid, X 2 is a neutral amino acid, X 3 is a neutral amino acid, X 4 is alanine, serine, Ai or Cn, X 5 is alanine, serine, Ai or Cn, X 6 is glutamine or alanine and X 7 is non-polar amino acid}, with the aspartic acids at position 3 and position 8 each independently replaced by a residue selected from the group consisting of tetrazole-substituted aspartic acid (Tz), tetrazole-substituted glutamic acid (egTz), tetrazole-substituted homoglutamic acid (nvTz), sulfoxy-substituted aspartic acid (cya) and oxadiazolone-substituted aspartic acid (SOxa), or its modified sequence, wherein the peptide has affinity for PAC1R and VPAC1R, and the modified sequence is the sequence listed as SEQ ID NO: 3, wherein: (A) 1 to 10 amino acids are added at the N-terminal end or C-terminal end, or (B) one sequence selected from the group consisting of the following: GKRYKQRVKNK (SEQ ID NO: 43); GKRYKQRVKN (SEQ ID NO: 44); GKRYKQRVK (SEQ ID NO: 45); GKRYKQRV (SEQ ID NO: 46); GKRYKQR (SEQ ID NO: 47); GKRYKQ (SEQ ID NO: 48); GKRYK (SEQ ID NO: 49); GKRY (SEQ ID NO: 50) GKR; GRR; GK; and GR G; is added to the C-terminus of the peptide, or (C) one or two, preferably one amino acid is deleted at the N-terminal or C-terminal end. (A) 1 to 10 amino acids are added at the N-terminal end or C-terminal end, or (B) one sequence selected from the group consisting of the following: GKRYKQRVKNK (SEQ ID NO: 43); GKRYKQRVKN (SEQ ID NO: 44); GKRYKQRVK (SEQ ID NO: 45); GKRYKQRV (SEQ ID NO: 46); GKRYKQR (SEQ ID NO: 47); GKRYKQ (SEQ ID NO: 48); GKRYK (SEQ ID NO: 49); GKRY (SEQ ID NO: 50) GKR; GRR; GK; and GR G; is added to the C-terminus of the peptide, or GKRYKQRVKNK (SEQ ID NO: 43); GKRYKQRVKN (SEQ ID NO: 44); GKRYKQRVK (SEQ ID NO: 45); GKRYKQRV (SEQ ID NO: 46); GKRYKQR (SEQ ID NO: 47); GKRYKQ (SEQ ID NO: 48); GKRYK (SEQ ID NO: 49); GKRY (SEQ ID NO: 50) GKR; GRR; GK; and GR G; is added to the C-terminus of the peptide, or (C) one or two, preferably one amino acid is deleted at the N-terminal or C-terminal end. <EOS>