A corrosion inhibitor for magnesium and/or magnesium alloy containing, as an effective component, a least one kind of compound selected from the group consisting of a compound of the formula (1) and a compound of the formula (2) and salts thereof, and a process for producing components or parts made of magnesium and/or magnesium alloy using the corrosion inhibitor wherein R1 is a hydrogen atom, or C1-4 alkyl, R2 is a hydrogen atom, C1-4 alkyl, mercapto or hydroxy, R3 is a hydrogen atom, C1-4 alkyl or hydroxy, A is —N═ or —C(R4)═, R4 is a hydrogen atom or amino.