PURPOSE: To obtain a metal surface treatment agent which can firmly adhere to a metal surface and can exhibit a rust-preventive action and water/oil repellency even in the form of this film by using a fluoropolymer obtained by polymerizing a compound having three carbonyl groups and at least one double bond.

CONSTITUTION: This metal surface treatment agent is obtained by using a polymer comprising repeating units of formula I (wherein R1 and R2 are each a 1-10C alkyl, provided that either of them is a fluoroalkyl; R3 is a bond or a 1-8C alkylene; (x), (y) and (z) are each 0 or 1) or a polymer obtained by polymerizing a fluorocompound having three carbonyl groups and at least one double bond and represented by formula II (wherein at least any one of R1, R2 and R4 is a 2-10C double-bond-terminated alkenyl or a 1-10C alkyl, and at least one of them is a fluoroalkyl; and (x), (y) and (z) are each 0 or 1) as the effective component. The keto tricarbonyl groups in the formulae should also include the enol ones of the corresponding tautomer. This polymer is used as a surface treatment agent of a metal in the form of a solution in e.g. in alcohol and is useful for particularly copper foils of printed boards, steel sheets and aluminum sheets.