It is intended to provide: a compound useful as an amyloid oxidation catalyst which is applicable in vivo and is applicable not only to A² peptides but to other amyloids and a prophylactic or therapeutic drug for an amyloid-related disease, comprising the same. The present invention provides a benzothiazole compound represented by the following formula (1) wherein X represents a halogen atom R 1 represents an optionally substituted hydrocarbon group R 2 represents a hydrogen atom or an optionally substituted hydrocarbon group R 3 and R 4 are the same or different and each represent a hydrogen atom, an optionally substituted hydrocarbon group, an alkoxy group, a halogen atom, an amino group, a nitro group, or a cyano group R 2 and R 4 optionally together form an alkylene group and R 5 represents an anion.
