A human serum albumin mutant-linked protein comprising a first polypeptide chain comprising the amino acid sequence of the human serum albumin mutant and a second polypeptide chain linked thereto comprising the amino acid sequence of another protein, wherein the human serum albumin mutant is selected from the group consisting of a human serum albumin mutant having the amino acid sequence set forth as SEQ ID NO:3, and a human serum albumin mutant comprising an amino acid sequence that, in comparison with the amino acid sequence set forth as SEQ ID NO:3, lacks 1 to 5 amino acid residues and/or has 1 to 5 amino acid residues replaced, with the proviso that the asparagine residue occurring at position 318 and the threonine at position 320 from the N-terminus of the amino acid sequence set forth as SEQ ID NO:3 are preserved and linked by peptide bonds via a single amino acid residue except proline that is placed between those two amino acid residues, and wherein the protein is selected from the group consisting of a wild type human 22K growth hormone having the amino acid sequence set forth as SEQ ID NO:9, a wild type human 20K growth hormone having the amino acid sequence set forth as SEQ ID NO:10, a 22K growth hormone mutant having 1-4 amino acids substituted, deleted, and/or added as compared to the amino acid sequence of the wild type human 22K growth hormone and yet having growth-promoting activity, and a 20K growth hormone mutant having 1-4 amino acids substituted, deleted, and/or added as compared to the amino acid sequence of the wild type human 20K growth hormone and yet having growth-promoting activity. the human serum albumin mutant is selected from the group consisting of a human serum albumin mutant having the amino acid sequence set forth as SEQ ID NO:3, and a human serum albumin mutant comprising an amino acid sequence that, in comparison with the amino acid sequence set forth as SEQ ID NO:3, lacks 1 to 5 amino acid residues and/or has 1 to 5 amino acid residues replaced, with the proviso that the asparagine residue occurring at position 318 and the threonine at position 320 from the N-terminus of the amino acid sequence set forth as SEQ ID NO:3 are preserved and linked by peptide bonds via a single amino acid residue except proline that is placed between those two amino acid residues, and a human serum albumin mutant having the amino acid sequence set forth as SEQ ID NO:3, and a human serum albumin mutant comprising an amino acid sequence that, in comparison with the amino acid sequence set forth as SEQ ID NO:3, lacks 1 to 5 amino acid residues and/or has 1 to 5 amino acid residues replaced, with the proviso that the asparagine residue occurring at position 318 and the threonine at position 320 from the N-terminus of the amino acid sequence set forth as SEQ ID NO:3 are preserved and linked by peptide bonds via a single amino acid residue except proline that is placed between those two amino acid residues, and wherein the protein is selected from the group consisting of a wild type human 22K growth hormone having the amino acid sequence set forth as SEQ ID NO:9, a wild type human 20K growth hormone having the amino acid sequence set forth as SEQ ID NO:10, a 22K growth hormone mutant having 1-4 amino acids substituted, deleted, and/or added as compared to the amino acid sequence of the wild type human 22K growth hormone and yet having growth-promoting activity, and a 20K growth hormone mutant having 1-4 amino acids substituted, deleted, and/or added as compared to the amino acid sequence of the wild type human 20K growth hormone and yet having growth-promoting activity. a wild type human 22K growth hormone having the amino acid sequence set forth as SEQ ID NO:9, a wild type human 20K growth hormone having the amino acid sequence set forth as SEQ ID NO:10, a 22K growth hormone mutant having 1-4 amino acids substituted, deleted, and/or added as compared to the amino acid sequence of the wild type human 22K growth hormone and yet having growth-promoting activity, and a 20K growth hormone mutant having 1-4 amino acids substituted, deleted, and/or added as compared to the amino acid sequence of the wild type human 20K growth hormone and yet having growth-promoting activity.