Nowadays, eco-driving as a series of driving behaviors is proposed to reduce CO₂ discharge of vehicle and realize safe driving. The eco-driving behaviors are mainly about accelerator and brake works that are operated by leg`s motions of driver; however, there are few studies to explain physical fatigue resulted by leg`s motions for eco-driving behaviors. In the paper, eco-driving experiment was conducted in the modes of normal driving, eco-driving with instruction, and eco-driving with eco-indicator. The simulated driving experiment was realized by a universal driving simulator system, and surface electromyography of leg muscle of 10 subjects was measured to clarify physical fatigue of driver in different driving modes. The experiment indicates that fuel economy in eco-driving with eco-indicator is higher than other driving modes, and muscle activities are lowest by signal analysis of the surface electromyography. The result also suggests that eco-indicator is effective assistant system to help driver realize eco-driving as well as reduce physical burden of driver.