There are provided an engine controlling section 141 for controlling a rotational speed of an engine 18, a horizontal position controlling section 421 for rendering a vehicle body frame 10 to a horizontal position by controlling a position changing mechanism 200 configured to change a position of the vehicle body frame 10 by an operation of an actuator utilizing power from the engine 18, a yield measuring section 144 for measuring a yield of grains stored in a grain tank 5 based on measurement result of a load cell 60 configured to measure a weight of the grain tank 5, an activation operational tool 9a for outputting an activation signal for activating yield measurement by the yield measuring section 144, and a yield controlling section 153 configured to provide the engine controlling section 141 with a high speed rotation instruction for driving the engine 18 at a rated rotational speed in response to the activation signal and also to provide the horizontal position controlling section 421 with a horizontal position instruction for rendering the vehicle body frame 1 to the horizontal position.
