Disclosed is a novel renin-active substance by utilizing a anti-peptide antibody capable of specifically recognizing a specific amino acid sequence in the human prorenin profragment exemplified, as a typical example, by a complex formed from human prorenin and an anti-peptide antibody capable of specifically recognizing an amino acid sequence consisting of at least 15 amino acid residues located within an amino acid sequence consisting of 33 amino acid residues between the isoleucine residue at the 11th site and the arginine residue at the 43rd site within human prorenin profragment having an amino acid sequence consisting of 43 amino acid residues.