When an n speed prohibition command is being output from the AI shift controlling component, the AI shift control is performed even in the S mode if the vehicle speed V is lower than the reference vehicle speed Vn, whereby busy shifting can be effectively prevented when the vehicle is running on an uphill road or cornering. When the vehicle speed V is equal to or higher than the reference vehicle speed Vn, the AI shift control is cancelled, thus minimizing the possibility of a large engine brake force being applied to the vehicle despite the intention of the driver.