Aquinolone compound represented by the following Formula for use in the therapy and/or prophylaxis of neurodegenerative diseases, diseases induced by neurological dysfunction, or diseases induced by deterioration of mitochondrial function: or a salt thereof, wherein: R 1 represents hydrogen; R 2 represents hydrogen or C 1 -C 6 alkyl; and R 3 represents phenyl, naphthyl, pyridyl, furyl, thienyl, indolyl, benzodioxolyl or benzothienyl, wherein the aromatic or heterocyclic ring represented by R 3 may be substituted with one or more substituents selected from the group consisting of the following substituents to: C 1 -C 6 alkyl, halogen-substituted C 1 -C 6 alkyl, C 1 -C 6 alkoxy, halogen-substituted C 1 -C 6 alkoxy, phenyl optionally having one or more substituents selected from the group consisting of C 1 -C 6 alkyl and C 1 -C 6 alkoxy, and halogen; R 4 represents hydrogen, C 1 -C 6 alkyl, halogen-substituted C 1 -C 6 alkyl, C 1 -C 6 alkoxy, C 1 -C 6 alkoxy C 1 -C 6 alkyl, phenyl, cyclo C 3 -C 8 alkyl, or carbamoyl optionally having one or two C 1 -C 6 alkyl groups; R 5 represents hydrogen, C 1 -C 6 alkyl, halogen, C 1 -C 6 alkoxy, benzoylamino, or imidazolyl, R 6 represents hydrogen, halogen, C 1 -C 6 alkyl, or C 1 -C 6 alkoxy; and R 7 represents any of the following groups to: C 1 -C 6 alkyl, C 1 -C 6 alkoxy, phenoxy, cyclo C 3 -C 8 alkyloxy, halogen, C 1 -C 6 alkylthio, amino optionally having one or two substituents selected from the group consisting of C 1 -C 6 alkyl, C 1 -C 6 alkoxy C 1 -C 6 alkyl, and cyclo C 3 -C 8 alkyl, carbamoyl optionally having one or two C 1 -C 6 alkyl groups, pyrrolidinyl, azepanyl, morpholinyl, piperazinyl optionally having one or two C 1 -C 6 alkyl groups, imidazolyl optionally having one or two C 1 -C 6 alkyl groups, furyl, thienyl, benzothienyl, and pyrrolidinylcarbonyl. R 1 represents hydrogen; R 2 represents hydrogen or C 1 -C 6 alkyl; and R 3 represents phenyl, naphthyl, pyridyl, furyl, thienyl, indolyl, benzodioxolyl or benzothienyl, wherein the aromatic or heterocyclic ring represented by R 3 may be substituted with one or more substituents selected from the group consisting of the following substituents to: C 1 -C 6 alkyl, halogen-substituted C 1 -C 6 alkyl, C 1 -C 6 alkoxy, halogen-substituted C 1 -C 6 alkoxy, phenyl optionally having one or more substituents selected from the group consisting of C 1 -C 6 alkyl and C 1 -C 6 alkoxy, and halogen; C 1 -C 6 alkyl, halogen-substituted C 1 -C 6 alkyl, C 1 -C 6 alkoxy, halogen-substituted C 1 -C 6 alkoxy, phenyl optionally having one or more substituents selected from the group consisting of C 1 -C 6 alkyl and C 1 -C 6 alkoxy, and halogen; R 4 represents hydrogen, C 1 -C 6 alkyl, halogen-substituted C 1 -C 6 alkyl, C 1 -C 6 alkoxy, C 1 -C 6 alkoxy C 1 -C 6 alkyl, phenyl, cyclo C 3 -C 8 alkyl, or carbamoyl optionally having one or two C 1 -C 6 alkyl groups; R 5 represents hydrogen, C 1 -C 6 alkyl, halogen, C 1 -C 6 alkoxy, benzoylamino, or imidazolyl, R 6 represents hydrogen, halogen, C 1 -C 6 alkyl, or C 1 -C 6 alkoxy; and R 7 represents any of the following groups to: C 1 -C 6 alkyl, C 1 -C 6 alkoxy, phenoxy, cyclo C 3 -C 8 alkyloxy, halogen, C 1 -C 6 alkylthio, amino optionally having one or two substituents selected from the group consisting of C 1 -C 6 alkyl, C 1 -C 6 alkoxy C 1 -C 6 alkyl, and cyclo C 3 -C 8 alkyl, carbamoyl optionally having one or two C 1 -C 6 alkyl groups, pyrrolidinyl, azepanyl, morpholinyl, piperazinyl optionally having one or two C 1 -C 6 alkyl groups, imidazolyl optionally having one or two C 1 -C 6 alkyl groups, furyl, thienyl, benzothienyl, and pyrrolidinylcarbonyl. C 1 -C 6 alkyl, C 1 -C 6 alkoxy, phenoxy, cyclo C 3 -C 8 alkyloxy, halogen, C 1 -C 6 alkylthio, amino optionally having one or two substituents selected from the group consisting of C 1 -C 6 alkyl, C 1 -C 6 alkoxy C 1 -C 6 alkyl, and cyclo C 3 -C 8 alkyl, carbamoyl optionally having one or two C 1 -C 6 alkyl groups, pyrrolidinyl, azepanyl, morpholinyl, piperazinyl optionally having one or two C 1 -C 6 alkyl groups, imidazolyl optionally having one or two C 1 -C 6 alkyl groups, furyl, thienyl, benzothienyl, and pyrrolidinylcarbonyl.