The objective of the present invention is to provide a safe muscle-enhancing agent by which a muscle mass and muscular strength can be effectively increased or maintained and by which a decrease of a muscle mass and muscular strength can be suppressed, a muscle-enhancing composition containing the muscle-enhancing agent, and a method for enhancing muscle by using the muscle-enhancing agent or muscle-enhancing composition. The muscle-enhancing agent according to the present invention is characterized in comprising an extract derived from lemon myrtle as an active ingredient.
