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 radioactive halogen substituent, R2 is a group selected from the group consisting of hydrogen, a hydroxyl group, a methoxy group, a carboxyl group, an amino group, an N-methylamino group, an N,N-dimethylamino group and a cyano group, and p is an integer of 0 to 2, 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. A diagnostic agent for Alzheimer's disease contains the compound.