Disclosed are: an anti-fatigue agent comprising a dioxabicyclo[3.3.0]octanederivative such as sesamin contained in a sesame; and a pharmaceutical compositionand a functional food each comprising the anti-fatigue agent. The compound canbe administered to a human body or an animal safely and therefore can be ingestedcontinuously. The compound is effective for promoting the improvement in endurance,the increase in body strength, the relief of fatigue and the recovery from fatigue.