One or more compounds selected from the group consisting of compounds represented by the following formula: wherein R 1 represents a benzoylmethyl group whose benzene ring is unsubstituted or substituted by an alkyl group having 1 to 7 carbon atoms, an alkoxyl group having 1 to 7 carbon atoms, fluorine, and/or chlorine, an unsubstituted or fluorine-substituted linear or branched alkyl group having 4 to 6 carbon atoms, or phenyl group- or cyclopentyl group-substituted methylene or ethylene, wherein the phenyl group is optionally further substituted by one or more phenyl groups, R 2 substitutes positions 4, 5, 6, and/or 7 of indole and is selected from the group consisting of hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 7 carbon atoms, fluorine, and chlorine, R 3 represents any one group selected from OH, OR 4, NHR 4, and NR 4 R 5, and R 4 and R 5 are the same or different and each represents a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, the following formula: wherein R 6 represents hydrogen or a methyl group, X represents an alkylene group having 4 to 6 carbon atoms or an ether group having 4 carbon atoms, R 3 represents any one group selected from OH, OR 4, NHR 4, and NR 4 R 5, and R 4 and R 5 are the same or different and each represents a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and the following formula: wherein: R 3 represents any one group selected from OH, OR 4, NHR 4, and NR 4 R 5, and R 4 and R 5 are the same or different and each represents a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms; and (i) A represents naphthalene, and positions 1 and 7 of the naphthalene are each substituted by an acetic acid group and R 7 O, respectively, wherein R 7 represents an alkyl group having 1 to 5 carbon atoms or a benzyl group, wherein the benzene ring of the benzyl group is optionally substituted by one or more alkyl groups having 1 to 3 carbon atoms or alkoxyl groups having 1 to 3 carbon atoms; or (ii) A represents indole substituted at positions 3 and 5 by an acetic acid group and R 7 O, respectively or naphthalene substituted at positions 1 and 7 by an acetic acid group and R 7 O, respectively and R 7 represents a benzyl group, wherein the benzene ring of the benzyl group is optionally substituted by one or more alkyl groups having 1 to 3 carbon atoms or alkoxyl groups having 1 to 3 carbon atoms; and a pharmaceutically acceptable salt thereof when R 3 is OH, for use in the treatment of mitochondrial disease. (i) A represents naphthalene, and positions 1 and 7 of the naphthalene are each substituted by an acetic acid group and R 7 O, respectively, wherein R 7 represents an alkyl group having 1 to 5 carbon atoms or a benzyl group, wherein the benzene ring of the benzyl group is optionally substituted by one or more alkyl groups having 1 to 3 carbon atoms or alkoxyl groups having 1 to 3 carbon atoms; or (ii) A represents indole substituted at positions 3 and 5 by an acetic acid group and R 7 O, respectively or naphthalene substituted at positions 1 and 7 by an acetic acid group and R 7 O, respectively and R 7 represents a benzyl group, wherein the benzene ring of the benzyl group is optionally substituted by one or more alkyl groups having 1 to 3 carbon atoms or alkoxyl groups having 1 to 3 carbon atoms; and