Abstract: The present invention provides a mitochondrial activator containing pyrroloquinoline quinone, preferably pyrroloquinoline quinone and coenzyme Q (particularly reduced coenzyme Q) as active ingredients. In addition, the present invention provides a mitochondrial activator containing citric acid, preferably citric acid and coenzyme Q (particularly reduced coenzyme Q), as active ingredients. Since pyrroloquinoline quinone or citric acid exhibits a synergistic mitochondria activating effect with coenzyme Q (particularly reduced coenzyme Q), a high effect can be obtained even at a low dose. According to the present invention, therefore, a safer and practical mitochondrial activator is provided. The present invention further provides an agent for the prophylaxis or treatment of a disease caused by mitochondrial dysfunction.