In order to study the mechanical activity of a single cardiac myocyte under a wide range of load, we have developed a novel force measurement system using carbon fibers. Newly fabricated Graphite Reinforced by Carbon (GRC) fibers greatly facilitate the firm attachment of cell membrane to the fibers. A pair of fibers was attached to both ends of the cell; the rigid fiber as a mechanical ground and the compliant fiber for the strain gauge. By connecting the compliant fiber to the piezoelectric translator and applying the position signal to the driver, we could make the myocyte contract under isometric condition. Feedback control of the system also enabled us to study the relation between work output and the load. This system can be a useful tool in studying the mechanical activity of the cardiac myocyte under genetic as well as pharmacological interventions.