Disclosed are a curcumin derivative or a salt thereof, which contains a fluorine atom, represented by formula (I):(wherein R1a and R1b are each independently a hydrogen atom, alkyl, acetyl, or methoxycarbonyl R2s are each independently a fluorine atom, CHF2—, CF3—, CHF2O—, or CF3O— R3s are each independently a hydrogen atom or a fluorine atom A is alkyl, cyano, carboxyl, alkoxycarbonyl, or R4—(CH2)m— R4 is hydroxy, carboxy, cyano, acetyloxy, alkoxycarbonyl, alkoxyalkoxy, hydroxyalkoxy, or CONR5R6 R5 and R6 are each independently a hydrogen atom or alkyl and m is an integer from 1 to 5), and a diagnostic imaging agent for diagnosing a disease in which an amyloid β peptide aggregate accumulates, the diagnostic imaging agent containing a compound having a 1,3-dicarbonyl structure, wherein the compound exists in a keto form and an enol form, and the keto form and the enol form have different affinities, respectively, to the amyloid β peptide aggregate.
