A simple equivalent circuit model is employed to examine the ionosphere-magnetotail coupling during substorms. The Pedersen and Hall conductivities are assumed to be finite in the two resistive regions, which represent the mid-tail plasma sheet and the poleward half of the nightside auroral oval. These two regions are connected through both the wedge-current and meridional-current systems. It is demonstrated that this model successfully reproduces substorm changes in the cross-tail current and the westward electrojet. In consistent with earlier observations, the solutions of the model suggest that about 90% of the westward electrojet is the Hall current. It is shown that at the expansion onset of substorms the overshoot electric field is induced more effectively for a weaker increase in the ionospheric conductivity.