The present invention relates to a cellulase preparation comprising nonionic surfactants together with endoglucanases derived from Zygomycetes; a detergent composition comprising the above cellulase preparation with detergent components; a method of treating fabric which comprises treating cellulose-containing fabric with the above cellulase preparation so as to improve the properties of the fabric; a method of deinking waster paper which comprises a step of treating waste paper with the above cellulase preparation together with a deinking agent; and a method of improving the freeness of paper pulp which comprises a step of treating paper pulp with the above cellulase preparation.