The invention provides a reagent for detecting amyloid deposited in a biological tissue which can detect amyloid in vitro and in vivo with high sensitivity using a compound which has affinity with amyloid and is suppressed in toxicity such as mutagencity. The reagent for detecting amyloid deposited in a biological tissue comprises a compound represented by the following formula (1) or a salt thereof:wherein A1, A2, A3 and A4 independently represent carbon or nitrogen R1 is a radioactive halogen substituent R2 is a group selected from the group consisting of hydrogen, hydroxyl group, methoxy group, carboxyl group, amino group, N-methylamino group, N,N-dimethylamino group and cyano group and m is an integer of 0 to 2, provided that at least one of A1, A2, and A4 represents a carbon, and R1 binds to a carbon represented by A1, A2, A3 and A4.
