The present invention relates to a cleaning agent composition for use in cleaning a substrate for recording media, a substrate for photomask, or a substrate for flat panel display, a surface of which at least contains a metallic or glassy substrate moiety, the cleaning agent composition containing (I) a copolymer compound satisfying at least the following (i) to (iii): (i) a constituting unit A1 derived from acrylic acid is contained in an amount of 20% by mol or more of the entire constituting units; (ii) the constituting unit A1 derived from acrylic acid and a constituting A2 derived from 2-acrylamide-2-methylpropanesulfonic acid are contained in a total amount of 90% by mol or more of the entire constituting units; and (iii) the constituting unit A1 and the constituting unit A2 of the entire constituting units are in a content ratio [constituting unit A1 (% by mol)/constituting unit A2 (% by mol)] of from 91/9 to 95/5.