An automatic transmission (5) of a vehicle performs a downshift operation when a downshift signal is ON. When the downshift signal is ON, a controller (12) increases an output torque of an engine (1) so that a predetermined torque increase amount is realized. The controller (12) sets a torque increase permission period which is shorter, the larger the predetermined torque increase amount is (S209), and when the elapsed time from when the downshift signal is ON reaches the torque increase permission period, unnecessary increase of engine rotation speed and excessive torque load on the automatic transmission (5) are prevented by terminating increase of output torque (S211, S214).