Problem: to provide an activator for activating intracellular ATP production. Solution: use of a 5-deazaflavin compound represented by the following 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 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 each 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 alkylamino group, a phenyl-substituted lower alkylamino group, or a lower alkylsulfonyl group).
