The investigation of positional instabilities, that is, vertical displacement and horizontal expansion of the plasma loop, is extended to a tokamak with a resistive shell. The shell current induced by a small displacement of the current-carrying plasma column produces a restoring force, which contributes to the stabilization. The quantitative analysis of the effect due to the shell shows that the finiteness of the minor radius of the plasma column reduces the effective skin time of the shell τs from the intrinsic one. Consequently it is shown that although the stability condition is not altered, a resistive shell restrains the growth rate of the instability to the order of τs-1, in a wider region than the stable one.