Provision of a drug, a quasi-drug, and a food or beverage, which are effective for senescence inhibition, mitochondrial function improvement, muscle dysfunction inhibition, muscular atrophy inhibition, prevention of a bedridden state, muscle senescence inhibition, or motor function improvement. A senescence inhibitor, a mitochondrial function-improving agent, a muscle dysfunction inhibitor, a muscular atrophy inhibitor, and an agent for preventing a bedridden state, containing a catechin as an effective ingredient. A muscle senescence inhibitor and a motor function-improving agent, containing a catechin and an amino acid as effective ingredients.