A method for detecting a site where an N-linked glycan chain is linked and/or a site where an N-linked glycan chain is not linked in a glycoprotein, comprising: (A) removing an N-linked glycan chain from an N-linked glycosylated glycoprotein and changing an asparagine residue to which the N-linked glycan chain is linked to an aspartic acid residue; (B) hydrolyzing the glycoprotein obtained in step (A) to specifically hydrolyze either the asparagine residue or the aspartic acid residue to obtain peptide fragments; (C) detecting the peptide fragments obtained in step (B); and (D) by comparing with a peptide fragment obtained by hydrolyzing in the same manner as step (B) a protein having the same amino acid sequence as the original N-linked glycosylated glycoprotein but not having a glycan chain, judging that a glycan chain is linked to an N-linked glycosylation site in the case different peptide fragments are present among the peptide fragments detected in step (C) and the different peptide fragments are presumed to contain an N-linked glycosylation site or amino acid residue adjacent thereto, and/or judging that a glycan chain is not linked to an N-linked glycosylation site in the case identical peptide fragments are present among the peptide fragments detected in step (C) and those identical peptide fragments are presumed to contain an N-linked glycosylation site. (A) removing an N-linked glycan chain from an N-linked glycosylated glycoprotein and changing an asparagine residue to which the N-linked glycan chain is linked to an aspartic acid residue; (B) hydrolyzing the glycoprotein obtained in step (A) to specifically hydrolyze either the asparagine residue or the aspartic acid residue to obtain peptide fragments; (C) detecting the peptide fragments obtained in step (B); and (D) by comparing with a peptide fragment obtained by hydrolyzing in the same manner as step (B) a protein having the same amino acid sequence as the original N-linked glycosylated glycoprotein but not having a glycan chain, judging that a glycan chain is linked to an N-linked glycosylation site in the case different peptide fragments are present among the peptide fragments detected in step (C) and the different peptide fragments are presumed to contain an N-linked glycosylation site or amino acid residue adjacent thereto, and/or judging that a glycan chain is not linked to an N-linked glycosylation site in the case identical peptide fragments are present among the peptide fragments detected in step (C) and those identical peptide fragments are presumed to contain an N-linked glycosylation site. judging that a glycan chain is linked to an N-linked glycosylation site in the case different peptide fragments are present among the peptide fragments detected in step (C) and the different peptide fragments are presumed to contain an N-linked glycosylation site or amino acid residue adjacent thereto, and/or judging that a glycan chain is not linked to an N-linked glycosylation site in the case identical peptide fragments are present among the peptide fragments detected in step (C) and those identical peptide fragments are presumed to contain an N-linked glycosylation site. <EOS>