[Problem] To provide a surface treatment agent capable of forming a hydrophilic film, the agent having excellent hydrophilicity as well as draining performance (drying performance) and which can further suppress the formation of frost; a method for producing the film; and a film-equipped metal material having the film. [Solution] The problem is solved by a surface treatment agent in which an amphoteric poly(meth)acrylamide and a compound having at least two aldehyde groups are combined in a solvent.