A transmission system including an automatic transmission having a plurality of speed change modes, including at least a continuously variable speed change node and a steeping speed change mode, and a sub-transmission connected to the automatic transmission. The sub-transmission is capable of switching to one of a plurality of running ranges including at least a forward range, a neutral range, and a reverse range. The transmission system also includes a mode switch for selectively switching to one of the plurality of speed change modes of the automatic transmission, and a shift switch for switching from one speed change stage to another speed change when the stepping speed change mode is active. Functionally of the shift switch and the mode switch are collectively integrated into a common switch, and the common switch is selectively used as the shift switch or the mode switch.