Abstract: There is disclosed a combine harvester in which a traveling change speed mechanism is automatically controlled in response to workload variations in order to maintain the workload within a predetermined range. In normal circumstances, controls are effected on the basis of an average value of deviations from a control target value of values of the load sampled a predetermined number of times. A change speed operation is immediately effected in an amount corresponding to the deviations when a difference between a value of variation of the sampled values from sampled values obtained a previous time from sampled values obtained earlier is greater than a predetermined value.