In order to quantitatively evaluate running form focusing fluctuation of knee, position of the knee was measured by using high-speed camera and plantar load was also evaluated by using strain gage sensor during running on treadmill with speed of 4, 8 and 12 km/h. The obtained results show the knee periodically fluctuated crosswise direction during running and the fluctuation width increased with increase in running speed. In addition, the intensity of fluctuation of knee was related to fluctuation of plantar load.