Japan has a very high aging rate among developed countries. The increase of medical expenses in a super-aged society has become serious. It is important to maintain good quality of life (QOL) throughout life. One of the factors that lowers QOL of the elderly is a decline in mobility accompanied by a decrease in muscle strength such as sarcopenia. Many food and drug suppliers are developing products to prevent muscle weakness. In this study, we tried to establish a test system to evaluate effects of therapeutic agents on muscle weakness using aged mice. First, we compared the muscle weakness of 12, 40, 53, 79, 92, and 105-week-old C57BL/6J male mice using a small animal muscle strength measuring device (Aurora Scientific). Next, we measured blood and organ concentrations of AGEs, NT-proBNP, and MURF1, which are indicators of aging. Muscle pathology was also examined. Compared with 12-week mice, aged mice (79 to 92 weeks) showed significantly lower muscle strength. Finally, we tested the effects of nicotinamide mononucleotide (NMN, a precursor of NAD), which is recently attracted attention as a dietary supplement with potential anti-aging effects. Oral administration of NMN for 12 weeks showed preventive effect on muscle weakness in aged mice. The present test system would be useful to evaluate potential efficacy of newly developed therapeutic agents on muscle weakness in the elderlies.