To solve the problems on a working vehicle such as a tractor on which a sub transmission device may be provided in addition to a main transmission device for fine speed selection, that the sub transmission device should be operated after the working vehicle is stopped, resulting in poor operability and lower fuel economy due to frequent start/stop.

This working vehicle transmission mechanism 3 comprises a stepped main transmission device 16 for shifting motor power output from a motor 2 into a plurality of main speed stages. On the transmission downstream side of the main transmission device 16, a sub transmission device 17 is arranged for shifting power from the main transmission device 16 into a plurality of sub speed stages. On the transmission upstream side of the main transmission device 16, a preliminary transmission device 14 is arranged for shifting the motor power into a plurality of preliminary speed stages.