An object of the present invention is to provide proteinaceous protease inhibitors with moderate inhibitory activity. A proteinaceous protease inhibitor of the present invention includes an amino acid sequence (Y) or an amino acid sequence (Y′), the amino acid sequence (Y) being different from the amino acid sequence (A) of a proteinaceous protease inhibitor (BC), 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 (Y),wherein the proteinaceous protease inhibitor satisfies at least one of the following conditions (1) to (8):(1) the amino acid residue at a position corresponding to residue 12 of the amino acid sequence (A) in the amino acid sequence (Y) or (Y′) is an amino acid (X1) defined below；(2) the amino acid residue at a position corresponding to residue 38 of the amino acid sequence (A) in the amino acid sequence (Y) or (Y′) is an amino acid (X2) defined below；(3) the amino acid residue at a position corresponding to residue 48 of the amino acid sequence (A) in the amino acid sequence (Y) or (Y′) is an amino acid (X3) defined below；(4) the amino acid residue at a position corresponding to residue 50 of the amino acid sequence (A) in the amino acid sequence (Y) or (Y′) is an amino acid (X4) defined below；(5) the amino acid residue at a position corresponding to residue 51 of the amino acid sequence (A) in the amino acid sequence (Y) or (Y′) is an amino acid (X5) defined below；(6) the amino acid residue at a position corresponding to residue 52 of the amino acid sequence (A) in the amino acid sequence (Y) or (Y′) is an amino acid (X6) defined below；(7) the amino acid residue at a position corresponding to residue 53 of the amino acid sequence (A) in the amino acid sequence (Y) or (Y′) is an amino acid (X7) defined below；(8) the amino acid residue at a position corresponding to residue 70 of the amino acid se
