By combination of hydrophobic chromatography and strongly basic anion-exchange chromatography, a novel, highly hydrophobic β-glucosidase was successfully identified from Acremonium cellulolyticus. Further, a gene corresponding to the identified β-glucosidase was isolated. When multiple modifications were introduced into the base sequence of the gene, the gene was successfully expressed in Trichoderma viride at a high level, and the expression product successfully exhibited a high β-glucosidase activity.