PURPOSE: To obtain a transmission structure of a combine harvester capable of always smoothly carrying grain culms regardless of change of machine travelling speed by improvement of simple transmission structure.

CONSTITUTION: The transmission structure of combine harvester is constituted so as to gather grain culms reaped by a reaping device along the direction of reaping width by an auger and then rake up and carry these grain culms toward the backward thresher by a feed conveyer 10. In this transmission, power is fed through one-way rotation clutch 16 by which rotation of the power after gear change of a hydrostatic transmission(HST) for machine body traveling is transmitted only to the advancing direction to a driving shaft 14 of the feed conveyer 10 and simultaneously a power from an engine E is transmitted to the driving shaft 14 and a rotation shaft 24 rotated at the prescribed number of revolutions is interlocked through one-way rotation clutch 25 with the driving shaft 14.