Disclosed is a benzothiophene oxide derivative represented by the general formula (wherein R1 and R2 are the same or different and each represents one or more groups selected from a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an aralkyl group, an alkoxy group, an aryloxy group, an alkenyl group, an amino group, a heterocyclic group, an amino group, a hydroxyl group, a carboxyl group, an oxo group and the like; R3 represents an alkylamino group, an amino group, a hydroxyl group or the like; and m and n are the same or different and each represents an integer of 1-6) or a salt thereof, which is useful as a prodrug of a benzothiophene derivative or a salt thereof.