An immunoglobulin-binding protein having an increased immunoglobulin-binding capacity, comprising at least one modified immunoglobulin-binding domain, wherein the at least one modified immunoglobulin-binding domain is selected from the group consisting of the following: a polypeptide being an immunoglobulin-binding domain consisting of an amino acid sequence set forth in SEQ ID NO: 1 or an amino acid sequence having at least 70% identity with the amino acid sequence set forth in SEQ ID NO: 1, wherein at least one amino acid residue is inserted between positions corresponding to the position 3 and position 4 of the amino acid sequence set forth in SEQ ID NO: 1, wherein the amino acid insertion results in the increased immunoglobulin-binding capacity of the immunoglobulin-binding protein; a polypeptide being an immunoglobulin-binding domain consisting of an amino acid sequence set forth in SEQ ID NO: 2 or an amino acid sequence having at least 70% identity with the amino acid sequence set forth in SEQ ID NO: 2, wherein at least one amino acid residue is inserted between positions corresponding to the position 3 and position 4 of the amino acid sequence set forth in SEQ ID NO: 2, wherein the amino acid insertion results in the increased immunoglobulin-binding capacity of the immunoglobulin-binding protein; and a polypeptide being an immunoglobulin-binding domain consisting of an amino acid sequence set forth in SEQ ID NO: 3 or an amino acid sequence having at least 70% identity with the amino acid sequence set forth in SEQ ID NO: 3, wherein at least one amino acid residue is inserted between positions corresponding to the position 3 and position 4 of the amino acid sequence set forth in SEQ ID NO: 3, wherein the amino acid insertion results in the increased immunoglobulin-binding capacity of the immunoglobulin-binding protein. a polypeptide being an immunoglobulin-binding domain consisting of an amino acid sequence set forth in SEQ ID NO: 1 or an amino acid sequence having at least 70% identity with the amino acid sequence set forth in SEQ ID NO: 1, wherein at least one amino acid residue is inserted between positions corresponding to the position 3 and position 4 of the amino acid sequence set forth in SEQ ID NO: 1, wherein the amino acid insertion results in the increased immunoglobulin-binding capacity of the immunoglobulin-binding protein; a polypeptide being an immunoglobulin-binding domain consisting of an amino acid sequence set forth in SEQ ID NO: 2 or an amino acid sequence having at least 70% identity with the amino acid sequence set forth in SEQ ID NO: 2, wherein at least one amino acid residue is inserted between positions corresponding to the position 3 and position 4 of the amino acid sequence set forth in SEQ ID NO: 2, wherein the amino acid insertion results in the increased immunoglobulin-binding capacity of the immunoglobulin-binding protein; and a polypeptide being an immunoglobulin-binding domain consisting of an amino acid sequence set forth in SEQ ID NO: 3 or an amino acid sequence having at least 70% identity with the amino acid sequence set forth in SEQ ID NO: 3, wherein at least one amino acid residue is inserted between positions corresponding to the position 3 and position 4 of the amino acid sequence set forth in SEQ ID NO: 3, wherein the amino acid insertion results in the increased immunoglobulin-binding capacity of the immunoglobulin-binding protein.