The present invention provides a means capable of efficiently manufacturing a fused substance of an Fc protein and a substance of interest (for example, a peptide). Specifically, the present invention provides an azide group-containing Fc protein represented by the following formula (1): €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒN 3 -L a -Phe-L b -Fc€ƒ€ƒ€ƒ€ƒ€ƒ(1) wherein N 3 represents an azide group； L a represents a bond or a divalent group； Phe represents a residue of phenylalanine or a derivative thereof； L b represents a lysine residue or an arginine residue, or a peptide linker consisting of two or more amino acid residues having a lysine residue or an arginine residue at/on the N-terminus； and Fc represents an Fc protein； and the like.
