By treating a material to be treated with a multifunctional surface-treatment agent composition containing octadecyldimethyl(3-trimethoxysilylpropyl)ammonium chloride and/or octadecyldimethyl(3-triethoxysilylpropyl)ammonium chloride, an amido amine oxide, an alcohol, and water, cloudiness and precipitation occurring during low-temperature storage is prevented antibacterial properties are exhibited deodorization properties, water repellency, and oil repellency are improved and frictional resistance is reduced.
