Abstract: A mobile agricultural machine has a pair of right and left traction members (2), a transmission (23,24), a main speed change device (68) operable to transmit at any speed ratio a driving force from an engine (21) through the transmission to the traction members so that the traction members are driven at any traveling speeds. The machine further has a steerage (26,27), and a steering device (19) operable to cause the steerage to differentiate the traveling speeds between the traction members (2). The traveling speeds are reduced in response to an extent to which the steering device (19) is operated, so that the agricultural machine running straight for an agricultural work along its running course that is being adjusted may smoothly be controlled merely by a continuous manual operation to make a spinning turn on a bare end of the farm for the next course of the work.