A tetrahydroisoquinolin-1-one derivative represented by formula (I) or a pharmaceutically acceptable salt thereof: wherein the symbols in the formula have the following meanings: ** Formula ** R1: (C1-6 alkylene which may be substituted with a group selected from the group consisting of phenyl which may be substituted with halogen, C1-6 alkyl or -OR0 and -OH) -OH, or cycloalkyl substituted with a group selected from the group consisting of -OR0, - N ( R0) 2, -N (R0) C (O) R0, -N (R0) C (O) -C 1-6 alkyl-OR0, -N (R0) S (O) 2- C1-6 alkyl and a group heterocyclic, R0: the same or different from each other, which each represents -H or C1-6 alkyl, R2: phenyl which may be substituted with halogen or -OR0, R3: -H, R4: -N (R0) -O -C1-6 alkylene (aryl or heteroaryl, which may each be substituted with a group selected from the group G6), Group G6: halogen, C1-6 alkyl which may be substituted with -OR0, halogen-C1-6 alkyl which may be substituted with -OR0, -CN, -N (R0 ) 2, -CO2R0, -CO2-alkylene C1-6-aryl, -C (O) N (R0) 2, alkylene C1-6-OC (O) R0, alkylene C1-6-OC (O) aryl, alkylene C1-6-CO2R0, halogen-alkylene C1-6-CO2R0, alkylene C1-6-CO2-alkylene C1-6-aryl, alkylene C1-6-C (O) N (R0) 2, halogen-alkylene C1-6 -C (O) N (R0) 2, -O-alkylene C1-6-CO2R0, -O-alkylene C1-6-CO2-alkylene C1-6-aryl, -O-alkylene C1-6-C (O) N (R0) 2, -O-halogen-alkylene C1-6-CO2R0, -O-halogen-alkylene C1-6-C (O) N (R0) 2, -C (O) N (R0) S (O ) 2-C1-6 alkyl, C1-6-C (O) N (R0) S (O) 2-C1-6 alkyl, -S (O) 2-C1-6 alkyl, -S (O) 2N (R0) 2, heterocyclic group, -C (>； = NH) NH2, -C (-NH)>； = NO-C (O) O-C1-10 alkyl, -C (>； = NOH) NH2, -C ( O) N>； = C (N (R0) 2) 2, -N (R0) C (O) R0, -N (R0) C (O) -alkyl C1-6-OR0, -N (R0) C ( O) OR0, -N (R0) S (O) 2-C1-6 alkyl, -C (aryl) 3 and oxo, whereby the "aryl" and the "heterocyclic group" in Group G6 can each be substituted with a group selected from the group consisting of halogen, C1-6 alkyl, halogen-C1-6 alkyl, -OR0, -O-halogen-C1-6 alkyl, oxo, and thioxo (>； = S)
