Abstract: Disclosed is a moisturizing agent comprising a copolymer represented by formula (1). [In formula (1), A represents a substituent containing an oligosaccharide composed of 2 to 6 monosaccharide molecules bound to each other; B represents a group represented by formula (2); m and n represent numbers which meet the following equation m:n=9:1 to 1:9; and Z represents a hydrogen group, a methyl group or an ethyl group.