A proteinaceous protease inhibitor comprising an amino acid sequence or an amino acid sequence (Y'), the amino acid sequence being different from the amino acid sequence of a proteinaceous protease inhibitor, represented by SEQ ID NO:1, by one to eight amino acid replacements with amino acids different from replaced amino acids, the amino acid sequence (Y') having at least 80% homology to the amino acid sequence, wherein the proteinaceous protease inhibitor satisfies at least one of the following conditions to: the amino acid residue at a position corresponding to residue 12 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 38 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 48 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 50 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 51 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 52 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 53 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 70 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below:: any of amino acids other than Glu: any of the amino acids other than Val and Ile: Leu or Thr: Ala, Phe, Ile, Leu, Ser or Thr: Ala, Lys, His, Leu or Ser: any of the amino acids other than Ile: any of the amino acids other than Asp: any of the amino acids other than Arg; and: Ala, Arg, Asn, Asp, Cys, Gly, Gln, Glu, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, or Val. the amino acid residue at a position corresponding to residue 12 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 38 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 48 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 50 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 51 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 52 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 53 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below; the amino acid residue at a position corresponding to residue 70 of the amino acid sequence in the amino acid sequence or (Y') is an amino acid defined below:: any of amino acids other than Glu: any of the amino acids other than Val and Ile: Leu or Thr: Ala, Phe, Ile, Leu, Ser or Thr: Ala, Lys, His, Leu or Ser: any of the amino acids other than Ile: any of the amino acids other than Asp: any of the amino acids other than Arg; and: Ala, Arg, Asn, Asp, Cys, Gly, Gln, Glu, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, or Val.: any of amino acids other than Glu: any of the amino acids other than Val and Ile: Leu or Thr: Ala, Phe, Ile, Leu, Ser or Thr: Ala, Lys, His, Leu or Ser: any of the amino acids other than Ile: any of the amino acids other than Asp: any of the amino acids other than Arg; and: Ala, Arg, Asn, Asp, Cys, Gly, Gln, Glu, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, or Val.