Magnetic field data from the geostationary satellites GOES 2 and GOES 3 are examined to study the development of substorm activity in the near-earth nightside magnetosphere (around a radial distance of 6.6 RE). Substorm events are those in which a well-defined single onset is seen at low latitude on the ground. The field configuration change from more taillike to more dipolelike starts initially in a longitudinally localized region in association with the ground onset, and it develops westward and eastward, even when the simultaneous onset of the low-latitude positive bay is recorded in a wide longitudinal region on the ground. It is also found that the variation caused by the field-aligned current starts at the ground onset and reaches a peak at the time of the field change. The present results are consistent with the view that the substorm is associated with a disruption and subsequent conversion of the cross-tail current to the field-aligned current connected with the polar ionosphere. It is indicated that the cross-tail current near synchronous orbit and its disruption are important in producing the field configuration change at synchronous orbit.