Stability diagrams and time responses of the feedback control for vertical instability are obtained in the JFT-2M tokamak. The experimental results are in good agreement with a feedback theory based on the filament current plasma model taking account of the non-axisymmetric effect of the vacuum vessel. The vertical instability, with a growth rate of about 500 s−1, is successfully stabilized by feedback control of the plasma position with ordinary 12-phase thyristor power supplies; the elongation factor achieved amounts to up to κ = 1.7.