A thermostable β-xylosidase, having a β-xylosidase catalytic domain including: (A) a polypeptide including the amino acid sequence represented by SEQ ID NO: 1, 3 or 5, (B) a polypeptide including an amino acid sequence in which at least one amino acid has been deleted, substituted, or added in the amino acid sequence represented by SEQ ID NO: 1, 3 or 5, and having hydrolysis activity against a substrate of p-nitrophenyl-β-D-xylopyranoside at least under conditions of 80° C. and pH 4.0, or (C) a polypeptide including an amino acid sequence having 80% or greater sequence identity with the amino acid sequence represented by SEQ ID NO: 1, 3 or 5, and having hydrolysis activity against a substrate of p-nitrophenyl-β-D-xylopyranoside at least under conditions of 80° C. and pH 4.0.