To provide a rust-proof and corrosion-proof surface treatment method for an aluminum based metallic heat exchanger in which rust-proof and corrosion-proof effect for an aluminum based metal is enhanced at a low cost and rust-proof and corrosion-proof treatment can be performed uniformly even for a heat exchanger of intricate shape without impeding thermal conductivity.

After being assembled, an aluminum based metallic heat exchanger is immersed into solution containing tricarbonyl compound shown by a formula (where, R1 represents an alkylene group, R2 represent an alkyl group, R3 represents an alkyl group, R4 represents an alkylene group or -R5-M-(OR2)3, R5 represents an alkylene group, M represents Si or Ti, and x, y and z represent 0 or 1), and subjected to heat treatment at 100-200°C for 10 min or longer thus coating the surface of a fin material with tricarbonyl compound of 0.1-5 micron thick.