A transmission device for farm tractors is disclosed. In the transmission device, a hollow travelling drive shaft and a PTO drive internal shaft are substituted for a typical hollow PTO drive shaft and travelling internal shaft, respectively. The transmission device also has a splined flange for directly transmitting the engine power from the flywheel to the PTO drive internal shaft. In a main change gear unit, a hub sleeve and a main gear shifting shaft are forged into a single structure. A super low-speed change gear unit is connected to a sub-change gear through two sets of shafts capable of allowing the super low-speed change gear unit to be independently operated from the sub-speed change gear unit. The transmission device is thus selectively operated without performing any super low-speed changing action.
