A vehicle driven by electric motors has been expected to find uses as personal mobility vehicles. We have been developing an electric skateboard as a candidate of personal mobility vehicles in the future. It is necessary to control the center of gravity of a driver on the board for being a comfortable transportation. The control design requires knowledge of human body dynamics on lateral motion. As a first step, we developed an electric skateboard with load measuring devices and tried to clarify the mechanism of human body dynamics by impulse response. To analyze the human body dynamics precisely, we applied a velocity servo control instead of acceleration control. Comparing with previous studies, the electric skateboard can apply large external force to the subject. We assumed a model based on hip strategy which keeps upper trunk perpendicular to the horizon consequently. As a result, feedback parameters of posture control on free standing delay time could be derived.