1. A control apparatus for an automatic transmission of a vehicle including a gear ratio calculating unit for controlling the automatic transmission to transfer an output of an engine of the vehicle to driven wheels after changing the gear ratio, and calculating the gear ratio, and a speed-change control unit for controlling the gear ratio based on the result of the calculation, comprising: a target driving torque generating unit for generating a value of the target driving torque based on a adaptation coefficient indicative of a running state and a vehicle speed, a driving torque calculating unit for calculating a value of driving torque based on the adaptation coefficient, the vehicle speed and the engine speed, a correcting unit for obtaining a correcting value for correcting the value of the target driving torque based on the value of the driving torque calculated by said driving torque calculating unit and correcting the target driving torque, a gear-ratio-change-command unit for generating a gear-ratio-change-command based on the correction value obtained by said correcting means and commanding the change in the gear ratio, wherein said speed-change control unit changes the gear ratio based on the gear-ratio-change-command from the gear-ratio-change-command unit.