A downshift allowable vehicle speed is variably set according to a torque converter slippage amount. Specifically, a downshift allowable vehicle speed is variably set by, using a reference downshift allowable vehicle speed when the torque converter slippage amount is 0 and a gear ratio of the automatic transmission after a downshift, calculating an allowable vehicle speed correction amount based on the present torque converter slippage amount and the gear ratio after the downshift, and setting a value obtained by subtracting the allowable vehicle speed correction amount from the reference downshift allowable vehicle speed as the downshift allowable vehicle speed. By such setting, it is possible to set a higher downshift allowable vehicle speed as the torque converter slippage amount becomes smaller, so it is possible to expand a downshift allowable region when the manual gearshift mode is selected.