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