NOVELTY - A beta -glucosidase comprising a beta -glucosidase catalytic domain which comprises (a) a polypeptide comprising a 619 amino acid sequence (SEQ ID NO: 1) fully defined in the specification, (b) a polypeptide comprising an amino acid sequence of SEQ ID NO: 1 in which one or more amino acids are added, deleted or substituted, and having beta -glucosidase activity, or (c) a polypeptide an amino acid sequence exhibiting 91% or more sequence identity to an amino acid sequence of SEQ ID NO: 1, and having beta -glucosidase activity, is new.    USE - The beta -glucosidase is useful in cellulase mixture for producing a cellulose degradation product (all claimed).    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) polynucleotide comprising a region that encodes a beta -glucosidase catalytic domain which comprises (a) a base sequence that encodes a polypeptide comprising an amino acid sequence of SEQ ID NO: 1, (b) a base sequence that encodes a polypeptide comprising an amino acid sequence of SEQ ID NO: 1 in which one or more amino acids are added, deleted or substituted, and having beta -glucosidase activity, (c) a base sequence that encodes a polypeptide comprising an amino acid sequence exhibiting 91% or more sequence identity to an amino acid sequence of SEQ ID NO: 1, and having beta -glucosidase activity or (d) a base sequence of a polynucleotide comprising a base pair sequence capable of hybridizing under stringent conditions with a 1860 base pair sequence (SEQ ID NO: 2) fully defined in the specification, and being a base sequence that encodes a polypeptide having beta -glucosidase activity;    (2) expression vector, which is incorporated with the polynucleotide, and which is able to express a polypeptide having beta -glucosidase activity in a host cell;    (3) transformant introduced with the expression vector;    (4) method for producing a beta -glucosidase;    (5) cellulase mixture, comprising the beta -glucosidase, and at least one type of other cellulases; and    (6) method (M1) for producing a cellulose degradation product, involves generating a cellulose degradation product by contacting a cellulose-containing material with the beta -glucosidase.