Disclosed is a protein kinase C enhancer characterized by containing a benzothiophene alkyl ether derivative represented by the general formula below or a salt thereof. (In the formula, R1 and R2 may be the same or different and represent 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 optionally protected 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 may be the same or different and represent an integer of 1-6.) This protein kinase C enhancer is useful for treatment or prevention of various diseases associated with protein kinase C.