A method for specifically determining a glycated β-chain N-terminal of glycated hemoglobin using protease (i) and ketoamine oxidase (ii) without a separation operation, and which comprises the following reaction steps (iii) and/or (iv): (i) a protease selected from 1) to 4): 1) carboxypeptidase W 2) neutral proteinase from Bacillus sp. 3) carboxypeptidase A 4) thermolysin which protease cleaves 1-deoxyfructosyl-L-valyl-L-histidine from a fragment including a glycated β-chain N-terminal of glycated hemoglobin without substantially cleaving 1-deoxyfructosyl-L-valine and/or 1-deoxyfructosyl-L-valyl-L-leucine from a fragment including a glycated α-chain N-terminal of glycated hemoglobin; (ii) ketoamine oxidase which reacts with 1-deoxyfructosyl-L-valyl-L-histidine from a glycated β-chain N-terminal of glycated hemoglobin by the protease (i) and consists of amino acid having at least 75% homology to an amino acid sequence in SEQ ID NO:1; (iii) a reaction step wherein the protease (i) cleaves a glycated amino acid and/or a glycated peptide from a glycated β-chain N-terminal of glycated hemoglobin without substantially cleaving ε-1-deoxyfructosyl-L-lysine and/or a glycated peptide including ε-1-deoxyfructosyl-L-lysine, which the ketoamine oxidase (ii) reacts with, from glycated hemoglobin; (iv) a reaction step wherein detecting the glycated amino acid and/or glycated peptide cleaved from the glycated β-chain N-terminal of glycated hemoglobin using ketoamine oxidase (ii) that has a reactivity to ε-1-deoxyfructosyl-(α-benzyloxycarbonyl-L-lysine) is 30% or less compared with that to 1-deoxyfructosyl-L-valyl-L-histidine. (i) a protease selected from 1) to 4): 1) carboxypeptidase W 2) neutral proteinase from Bacillus sp. 3) carboxypeptidase A 4) thermolysin which protease cleaves 1-deoxyfructosyl-L-valyl-L-histidine from a fragment including a glycated β-chain N-terminal of glycated hemoglobin without substantially cleaving 1-deoxyfructosyl-L-valine and/or 1-deoxyfructosyl-L-valyl-L-leucine from a fragment including a glycated α-chain N-terminal of glycated hemoglobin; 1) carboxypeptidase W 2) neutral proteinase from Bacillus sp. 3) carboxypeptidase A 4) thermolysin which protease cleaves 1-deoxyfructosyl-L-valyl-L-histidine from a fragment including a glycated β-chain N-terminal of glycated hemoglobin without substantially cleaving 1-deoxyfructosyl-L-valine and/or 1-deoxyfructosyl-L-valyl-L-leucine from a fragment including a glycated α-chain N-terminal of glycated hemoglobin; (ii) ketoamine oxidase which reacts with 1-deoxyfructosyl-L-valyl-L-histidine from a glycated β-chain N-terminal of glycated hemoglobin by the protease (i) and consists of amino acid having at least 75% homology to an amino acid sequence in SEQ ID NO:1; (iii) a reaction step wherein the protease (i) cleaves a glycated amino acid and/or a glycated peptide from a glycated β-chain N-terminal of glycated hemoglobin without substantially cleaving ε-1-deoxyfructosyl-L-lysine and/or a glycated peptide including ε-1-deoxyfructosyl-L-lysine, which the ketoamine oxidase (ii) reacts with, from glycated hemoglobin; (iv) a reaction step wherein detecting the glycated amino acid and/or glycated peptide cleaved from the glycated β-chain N-terminal of glycated hemoglobin using ketoamine oxidase (ii) that has a reactivity to ε-1-deoxyfructosyl-(α-benzyloxycarbonyl-L-lysine) is 30% or less compared with that to 1-deoxyfructosyl-L-valyl-L-histidine.