This invention provides an amadoriase having improved specific activity on a glycated substrate, compared with conventional amadoriase. Provided is an amadoriase comprising a substitution of the amino acid at the position corresponding to position 64 of the amino acid sequence as shown in SEQ ID NO: 1 with an amino acid selected from the group consisting of glycine, serine, methionine, leucine, threonine, valine, and isoleucine, a method for measurement of HbA1c, and a reagent kit for measurement of HbA1c using such amadoriase. Such method and kit for measurement enable rapid, simple, and accurate quantification of HbA1c.