A compound represented by the following formula or a salt thereof: wherein each of A1, A2, A3 and A4 independently represents a carbon or nitrogen; R1 is a group selected from the group consisting of hydrogen, hydroxyl group, carboxyl group, sulfuric acid group, amino group, nitro group, cyano group, non-radioactive halogen substituents, alkyl substituents with 1-4 carbon atoms and alkoxy substituents with 1-4 carbon atoms; and R2 is a radioactive halogen substituent, provided at least one of A1, A2, A3 and A4 represents a carbon, and R1 binds to a carbon represented by A1, A2, A3 or A4, is effective as an image diagnosis probe targeting amyloid and as well as a diagnostic agent for Alzheimer's disease including the compound represented by the above formula or a salt thereof.