Provided is a mutant β-glucosidase capable of more efficiently saccharifying biomass. A mutant β-glucosidase comprising an amino acid sequence having at least 80% sequence identity to SEQ ID NO: 1, wherein the amino acid sequence has asparagine at one or more positions selected from the group consisting of positions corresponding to positions 787, 790, and 797 of SEQ ID NO: 1, and has β-glucosidase activity.