Problem: To provide an activator for activating the production of ATP in a cell. Solution: A use of a 5-deazaflavin compound represented by formula (I) (wherein R1 represents a hydrogen atom, an alkyl group, a halogen-substituted alkyl group, a carboxy-substituted alkyl group or a phenyl group； R2 represents an alkyl group, a cycloalkyl group, a phenyl-substituted lower alkyl group, a phenyl group, a phenyl group substituted by any one of a halogen atom, a lower alkyl group or a lower alkoxy group, or a (lower alkyl)-disubstituted phenyl group； and R3 and R4 independently represent a hydrogen atom, a lower alkyl group, a halogen atom, a hydroxyl group, a nitro group, a cyano group, a lower alkoxy group, a phenyl-substituted lower alkoxy, a (lower alkyl)amino group, a phenyl-substituted (lower alkyl)amino group or a (lower alkyl)sulfonyl group).本發明提供一種用於激活細胞中ATP產生的激活劑。一種式（I）所示的5-去氮黃素化合物的用途。式中，R1表示氫原子、烷基、鹵素取代烷基、羧基取代烷基、或苯基，R2表示烷基、環烷基、苯基取代低級烷基、苯基、經鹵素原子或低級烷基或低級烷氧基中的一個取代而成的苯基、低級烷基二取代苯基，R3及R4表示氫原子、低級烷基、鹵素原子、羥基、硝基、氰基、低級烷氧基、苯基取代低級烷氧基、低級烷基胺基、苯基取代低級烷基胺基、或低級烷基磺醯基。
