[en] The feedback control system of JT-60 has been studied for control variables of plasma current I sub(p), horizontal position R sub(p) and circular-cross-section deviation delta. The linearized mathematical model is useful for design of the feedback controllers. Simulation of the feedback control system was made assuming time evolution of various plasma parameters. Feedback control of each variable is satisfactory, and the feedback loop of each coil voltage is effective in reducing the influence of voltage fluctuation. Design of the feedback system of coil voltage is also described. (auth.)