To provide an improved β-fructofuranosidase which is capable of efficiently producing kestose while inhibiting the production of nystose. This improved β-fructofuranosidase comprises either: an amino acid sequence (a) obtained by introducing, into the amino acid sequence represented by SEQ ID NO: 2, an amino acid mutation i) in which the 85th glycine (G) from the N-terminal is substituted for a protein-constituting amino acid other than glycine (G), and/or an amino acid mutation ii) in which the 310th histidine (H) from the N-terminal is substituted for lysine (K), arginine (R), or tyrosine (Y); or an amino acid sequence (b) which exhibits β-fructofuranosidase activity, and which comprises an amino acid sequence obtained by deleting, substituting, inserting, or adding one or more amino acids in (a) other than the amino acid into which the amino acid mutation has been introduced.