A tetrahydroisoquinolin-1-one derivative represented by the formula or a pharmaceutically acceptable salt thereof: wherein the symbols in the formula represent the following meanings: R 1: (C 1-6 alkylene which may be substituted with a group selected from the group consisting of phenyl which may be substituted with halogen, C 1-6 alkyl or -OR 0, and -OH)-OH, or cycloalkyl substituted with a group selected from the group consisting of -OR 0, - N(R 0) 2, -N(R 0)C R 0, -N(R 0)C - C 1-6 alkylene-OR 0, -N(R 0)S 2 - C 1-6 alkyl, and a heterocyclic group, R 0: the same as or different from each other, each representing -H or C 1-6 alkyl, R 2: phenyl which may be substituted with halogen or -OR 0, R 3: -H, R 4: -N(R 0)-O-C 1-6 alkylene-(aryl or heteroaryl, which may be each substituted with a group selected from the group G 6), Group G 6: halogen, C 1-6 alkyl which may be substituted with -OR 0, halogeno-C 1-6 alkyl which may be substituted with -OR 0, -CN, -N(R 0) 2, -CO 2 R 0, -CO 2 - C 1-6 alkylene-aryl, -C N(R 0) 2, C 1-6 alkylene-OC R 0, C 1-6 alkylene-OC aryl, C 1-6 alkylene-CO 2 R 0, halogeno-C 1-6 alkylene-CO 2 R 0, C 1-6 alkylene-CO 2 - C 1-6 alkylene-aryl, C 1-6 alkylene-C N(R 0) 2, halogeno-C 1-6 alkylene-C N(R 0) 2, -O-C 1-6 alkylene-CO 2 R 0, -O- C 1-6 alkylene-CO 2 -C 1-6 alkylene-aryl, -O-C 1-6 alkylene-C N(R 0) 2, -O-halogeno-C 1-6 alkylene-CO 2 R 0, -O-halogeno-C 1-6 alkylene-C N(R 0) 2, -C N(R 0)S 2 - C 1-6 alkyl, C 1-6 alkylene-C N(R 0)S 2 -C 1-6 alkyl, -S 2 -C 1-6 alkyl, -S 2 N(R 0) 2, heterocyclic group, -C(=NH)NH 2, -C(-NH)=NO-C O-C 1-10 alkyl, -C(=NOH)NH 2, - C N=C(N(R 0) 2) 2, -N(R 0)C R 0, -N(R 0)C -C 1-6 alkylene-OR 0, -N(R 0)C OR 0, -N(R 0)S 2 -C 1-6 alkyl, -C(aryl) 3, and oxo, whereby the "aryl" and the "heterocyclic group" in Group G 6 may each be substituted with a group selected from the group consisting of halogen, C 1-6 alkyl, halogeno- C 1-6 alkyl, -OR 0, -O-halogeno-C 1-6 alkyl, oxo, and thioxo (=S), m: an integer of 0 to 3, and R 5: C 1-6 alkyl, halogeno- C 1-6 alkyl, halogen, nitro, -OR 0, -O-halogeno- C 1-6 alkyl, -N(R 0) 2, -O- C 1-6 alkylene-CO 2 R 0, or -O-C 1-6 alkylene-aryl, wherein the aryl in R 5 may be substituted with a group selected from the group consisting of halogen, C 1-6 alkyl, halogeno-C 1-6 alkyl, -OR 0 and -O-halogeno-C 1-6 alkyl. R 1: (C 1-6 alkylene which may be substituted with a group selected from the group consisting of phenyl which may be substituted with halogen, C 1-6 alkyl or -OR 0, and -OH)-OH, or cycloalkyl substituted with a group selected from the group consisting of -OR 0, - N(R 0) 2, -N(R 0)C R 0, -N(R 0)C - C 1-6 alkylene-OR 0, -N(R 0)S 2 - C 1-6 alkyl, and a heterocyclic group, R 0: the same as or different from each other, each representing -H or C 1-6 alkyl, R 2: phenyl which may be substituted with halogen or -OR 0, R 3: -H, R 4: -N(R 0)-O-C 1-6 alkylene-(aryl or heteroaryl, which may be each substituted with a group selected from the group G 6), Group G 6: halogen, C 1-6 alkyl which may be substituted with -OR 0, halogeno-C 1-6 alkyl which may be substituted with -OR 0, -CN, -N(R 0) 2, -CO 2 R 0, -CO 2 - C 1-6 alkylene-aryl, -C N(R 0) 2, C 1-6 alkylene-OC R 0, C 1-6 alkylene-OC aryl, C 1-6 alkylene-CO 2 R 0, halogeno-C 1-6 alkylene-CO 2 R 0, C 1-6 alkylene-CO 2 - C 1-6 alkylene-aryl, C 1-6 alkylene-C N(R 0) 2, halogeno-C 1-6 alkylene-C N(R 0) 2, -O-C 1-6 alkylene-CO 2 R 0, -O- C 1-6 alkylene-CO 2 -C 1-6 alkylene-aryl, -O-C 1-6 alkylene-C N(R 0) 2, -O-halogeno-C 1-6 alkylene-CO 2 R 0, -O-halogeno-C 1-6 alkylene-C N(R 0) 2, -C N(R 0)S 2 - C 1-6 alkyl, C 1-6 alkylene-C N(R 0)S 2 -C 1-6 alkyl, -S 2 -C 1-6 alkyl, -S 2 N(R 0) 2, heterocyclic group, -C(=NH)NH 2, -C(-NH)=NO-C O-C 1-10 alkyl, -C(=NOH)NH 2, - C N=C(N(R 0) 2) 2, -N(R 0)C R 0, -N(R 0)C -C 1-6 alkylene-OR 0, -N(R 0)C OR 0, -N(R 0)S 2 -C 1-6 alkyl, -C(aryl) 3, and oxo, whereby the "aryl" and the "heterocyclic group" in Group G 6 may each be substituted with a group selected from the group consisting of halogen, C 1-6 alkyl, halogeno- C 1-6 alkyl, -OR 0, -O-halogeno-C 1-6 alkyl, oxo, and thioxo (=S), m: an integer of 0 to 3, and R 5: C 1-6 alkyl, halogeno- C 1-6 alkyl, halogen, nitro, -OR 0, -O-halogeno- C 1-6 alkyl, -N(R 0) 2, -O- C 1-6 alkylene-CO 2 R 0, or -O-C 1-6 alkylene-aryl, wherein the aryl in R 5 may be substituted with a group selected from the group consisting of halogen, C 1-6 alkyl, halogeno-C 1-6 alkyl, -OR 0 and -O-halogeno-C 1-6 alkyl.