Disclosed are: a novel protein having an endoglucanase activity, which is found in a basidiomycete (into which edible mushrooms are classified) and is user-friendly from a safety standpoint and the like; novel DNA encoding the protein; a vector carrying the DNA; a transformant harboring the vector; a method for producing a protein having an endoglucanase activity by using the transformant; a method for producing a sugar by using at least one member selected from a protein having an endoglucanase activity and a basidiomycete; a method for producing ethanol by using a sugar produced by the aforementioned method; a food, a feed and a detergent each comprising a protein having an endoglucanase activity; and a method for treating a cellulose-containing woven fabric by using a protein having an endoglucanase activity. The protein is characterized by being derived from a basidiomycete, having a molecular weight of 18 kDa as determined by SDS-PAGE, and having an endoglucanase activity.