A working vehicle such as a mobile agricultural machine is designed such that it has an improved working efficiency if any spinning turn is not required, and has an improved running property in a wet farm. The vehicle has a pair of right and left crawlers (2), a speed change apparatus (25) for imparting traction force to the crawlers, a speed change lever (73) operable to control the speed change apparatus so as to alter running speed of the vehicle in a step-less manner. The vehicle further has a steering apparatus (28) and a steering wheel (19) operable to control the steering apparatus so as to alter difference in the running speeds between the crawlers (2). The running speed generally determined for each crawler by the speed change lever (73) can be decreased voluntarily and proportionally to an operated angle of the steering wheel (19).