Disclosed is a compound having affinity for amyloid, showing fully rapid clearance from a normal tissue, and reduced in toxicities including mutagenicity. Specifically, disclosed is a compound represented by the formula (1) or a salt thereof. Also disclosed is a low-toxic diagnostic agent for Alzheimer's disease, comprising a compound represented by the formula (1) or a salt thereof. (1) wherein A, A, A and A independently represent a carbon or a nitrogen； R represents a halogen substituent； R represents a halogen substituent； and m represents an integer ranging from 0 to 2, provided that at least one of R and R represents a radioactive halogen substituent, at least one of A, A, A and A represents a carbon, and R binds to A, A, A or A which represents a carbon.
