The present invention relates to provision of AMPK activating agent, endurance enhancing agent, and antifatigue agent, which have rich history of use in foods, high safety, readily available, and high workability, a method of activating AMPK, and a method of preventing, treating and/or ameliorating a life-style-related disease. The present invention provides AMPK activating agent, endurance enhancing agent, and antifatigue agent, each of which contains nootkatone as an active agent. The present invention provides a method of activating AMPK characterized by administering nootkatone in an effective amount, and a method of preventing, treating and/or ameliorating a life-style-related disease characterized by administering nootkatone in an effective amount.