The invention provides a water-system metal surface treatment agent which is used for forming a surface treatment film which is capable of preventing stripping of a laminated film or a resin coating from metal material and has excellent adhesion and chemical-resistant adhesion retentivity. The water-system metal surface treatment agent contains an organic compound (A) and one or more than one kind of cross-linking compounds (B); the molecular weight of the organic compound (A) is below 10000; each molecule of the organic compound (A) contains more than two carboxyl groups and/or hydroxyl groups, with the ratio being one group in 30~300 molecular weight; and the cross-linking compounds (B) are selected from cross-linking compounds (B1) containing structural units capable of reacting with the carboxyl groups and/or hydroxyl groups and cross-linking compounds (B2) containing elements capable of reacting with the carboxyl groups and/or hydroxyl groups.