A pyridinium salt having the formula (I):FORMULA (I)in which R3 is a methyl group; R4 is a hydrogen atom; m is an integer of 3; Z is -OR5; R5 is a methyl group; X is a pharmacologically acceptable anion; K is (1)-S- or (2)-S-S-R-; R is a straight-chain or branched alkyl group having 1-6 carbon atoms; J is a benzimidazole ring which may have a substituent (S); --- shows a bond thereby to connect wi