PROBLEM TO BE SOLVED: To provide a pharmaceutical or food and drink which inhibit myofunction decrease and muscle atrophy, are useful for preventing a bedridden state, and have a high level of safety.SOLUTION: An atrogin-1 gene expression inhibitor comprises gnetin C as an active ingredient. The expression of the atrogin-1 gene is inhibited, thereby preventing and improving disuse muscle atrophy, sarcopenia and the like, in order to prevent and improve muscle strength decrease.