To provide an improved protein of the outer membrane domain of a cell of protein G, having bondability to Fc region of immunoglobulin in a slightly acidic region and/or bondability to Fab region thereof reduced compared to that of the outer membrane domain of the cell of a wild-type protein G without damaging the high antibody-bonding activity in a neutral region.

The modified protein is obtained using an amino acid residue present within the distance of 6.5A from the Fc region as a mutation targeting site in the three-dimensional structural coordinate data of a complex obtained by bonding the outer membrane domain of the cell of the protein G with the Fc region of the immunoglobulin G, and having 40% exposed surface area rate, or an amino acid residue present in the Fab region or within 4A distance therefrom in the three-dimensional structural coordination data of a complex obtained by bonding the outer membrane domain of the cell of the protein G with the Fab region of the immunoglobulin G, and having 40% exposed surface area rate, and subjecting the amino acid residue to substitution with another amino acid residue. The substitutions can be combined.