A compound represented by the general formula (I) or a pharmaceutically acceptable salt thereof: ** Formula ** in which each substituent is defined as follows: R 1 represents a halogen atom, an allyl group, a cycloalkyl group C3-C6, or a C1-C6 alkyl group optionally substituted by one or two or more groups selected from the group of substituents a, wherein the group of substituents a consists of a C3-C6 cycloalkyl group, a hydroxyl group, a halogen atom, an oxo group, and a phenyl group； R2 represents a hydrogen atom； R3 represents a hydrogen atom； R4 represents a hydrogen atom or a methyl group； and A represents a piperidine group substituted by one or two or more groups selected from the group of substituents c, wherein the group of substituents c consists of a C1-C6 alkylsulfonyl group, an aminocarbonyl group, a C1-C6 di-alkylaminocarbonyl group , a C1-C6 alkoxy-C1-C6 alkylcarbonyl group, a C1-C6 di-alkylaminosulfonyl group, a C1-C6 alkylcarbonyl group optionally substituted by one or two or more groups selected from the substituent group d, a C1- alkoxycarbonyl group C6 optionally substituted by one or two or more groups selected from the group of substituents d, a heterocyclic group optionally substituted by one or two or more groups selected from the group of substituents d, a benzoyl group optionally substituted by one or two or more groups selected from the group of substituents d, and a benzoyl group optionally substituted by one or two or more groups selected from the group of substituents d, in which the g rupo of substituents d consists of a halogen atom, a carboxy group, an oxo group, an aminocarbonyl group, a C1-C6 alkoxy group, a C1-C6 alkoxycarbonyl group, a C1-C6 arylaminocarbonyl group, a C1-alkylaminocarbonyl C1 group -C6, a heterocyclocarbonyl group, a phenyl group, and a phenylaminocarbonyl group optionally substituted by one or two or more groups selected from the substituent group e, wherein the substituent group e consists of a heterocyclocar
