A compound represented by the following formula or a pharmaceutically acceptable acid addition salt thereof: wherein R is a hydrogen atom or a C 1-6 alkyl group optionally substituted with 1 to 3 fluorine atoms, wherein when R is a hydrogen atom, R 1 is a chlorine atom, a bromine atom, a trifluoromethyl group, an ethyl group, a trifluoromethoxy group, a methoxy group substituted with a phenyl group, a methoxy group substituted with a C 3-8 cycloalkyl group, an ethoxy group optionally substituted with 1 to 3 fluorine atoms, or C 3-8 cycloalkyloxy group, R 2 is a fluorine atom, a chlorine atom, a methyl group optionally substituted with 2 to 3 fluorine atoms, a methoxy group optionally substituted with 1 to 3 fluorine atoms, or an ethoxy group optionally substituted with 1 to 3 fluorine atoms, R 3 is a hydrogen atom or a methyl group, and R 4 is a fluorine atom or a methyl group optionally substituted with 1 to 3 fluorine atoms, or when R is a C 1-6 alkyl group optionally substituted with 1 to 3 fluorine atoms, R 1 is a hydrogen atom, a halogen atom, a C 1-6 alkyl group optionally substituted with 1 to 3 fluorine atoms, a C 1-6 alkoxy group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a C 3-8 cycloalkyl group, a C 3-8 cycloalkyloxy group, or a 4- to 6-membered heterocycloalkyloxy group, R 2 is a hydrogen atom, a cyano group, a halogen atom, a C 1-6 alkyl group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a hydroxyl group, or a C 1-6 alkoxy group optionally substituted with 1 to 3 substituents selected from a fluorine atom, a C 3-8 cycloalkyl group and a 4- to 6-membered heterocycloalkyl group, R 3 is a hydrogen atom or a C 1-6 alkyl group, and R 4 is a C 1-6 alkyl group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a hydroxyl group, or a C 1-6 alkoxy group. wherein R is a hydrogen atom or a C 1-6 alkyl group optionally substituted with 1 to 3 fluorine atoms, wherein when R is a hydrogen atom, R 1 is a chlorine atom, a bromine atom, a trifluoromethyl group, an ethyl group, a trifluoromethoxy group, a methoxy group substituted with a phenyl group, a methoxy group substituted with a C 3-8 cycloalkyl group, an ethoxy group optionally substituted with 1 to 3 fluorine atoms, or C 3-8 cycloalkyloxy group, R 2 is a fluorine atom, a chlorine atom, a methyl group optionally substituted with 2 to 3 fluorine atoms, a methoxy group optionally substituted with 1 to 3 fluorine atoms, or an ethoxy group optionally substituted with 1 to 3 fluorine atoms, R 3 is a hydrogen atom or a methyl group, and R 4 is a fluorine atom or a methyl group optionally substituted with 1 to 3 fluorine atoms, or R 1 is a chlorine atom, a bromine atom, a trifluoromethyl group, an ethyl group, a trifluoromethoxy group, a methoxy group substituted with a phenyl group, a methoxy group substituted with a C 3-8 cycloalkyl group, an ethoxy group optionally substituted with 1 to 3 fluorine atoms, or C 3-8 cycloalkyloxy group, R 2 is a fluorine atom, a chlorine atom, a methyl group optionally substituted with 2 to 3 fluorine atoms, a methoxy group optionally substituted with 1 to 3 fluorine atoms, or an ethoxy group optionally substituted with 1 to 3 fluorine atoms, R 3 is a hydrogen atom or a methyl group, and R 4 is a fluorine atom or a methyl group optionally substituted with 1 to 3 fluorine atoms, or when R is a C 1-6 alkyl group optionally substituted with 1 to 3 fluorine atoms, R 1 is a hydrogen atom, a halogen atom, a C 1-6 alkyl group optionally substituted with 1 to 3 fluorine atoms, a C 1-6 alkoxy group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a C 3-8 cycloalkyl group, a C 3-8 cycloalkyloxy group, or a 4- to 6-membered heterocycloalkyloxy group, R 2 is a hydrogen atom, a cyano group, a halogen atom, a C 1-6 alkyl group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a hydroxyl group, or a C 1-6 alkoxy group optionally substituted with 1 to 3 substituents selected from a fluorine atom, a C 3-8 cycloalkyl group and a 4- to 6-membered heterocycloalkyl group, R 3 is a hydrogen atom or a C 1-6 alkyl group, and R 4 is a C 1-6 alkyl group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a hydroxyl group, or a C 1-6 alkoxy group. R 1 is a hydrogen atom, a halogen atom, a C 1-6 alkyl group optionally substituted with 1 to 3 fluorine atoms, a C 1-6 alkoxy group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a C 3-8 cycloalkyl group, a C 3-8 cycloalkyloxy group, or a 4- to 6-membered heterocycloalkyloxy group, R 2 is a hydrogen atom, a cyano group, a halogen atom, a C 1-6 alkyl group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a hydroxyl group, or a C 1-6 alkoxy group optionally substituted with 1 to 3 substituents selected from a fluorine atom, a C 3-8 cycloalkyl group and a 4- to 6-membered heterocycloalkyl group, R 3 is a hydrogen atom or a C 1-6 alkyl group, and R 4 is a C 1-6 alkyl group optionally substituted with 1 to 3 substituents selected from a fluorine atom and a hydroxyl group, or a C 1-6 alkoxy group.