PURPOSE:To ensure the dimensional accuracy in transmitting constitution between a main counter case of a main transmission device and a threshing counter case and improve the installing rigidity of a thresher in an undercarriage and the supporting strength of an opening and supporting shaft of a feed chain. CONSTITUTION:This main transmission device in a combine harvester is obtained by integrally fixing a threshing counter case 4 to the top surface of a main counter case 6 and connecting supporting arms 10 of an opening and supporting shaft 9 for rotating and opening the threshing feed chain to the front to the top surface of the threshing counter case 4 in the combine harvester having the main counter case 6, containing a main transmission mechanism capable of inputting a power from an engine and transmitting the power to a mobile device and a reaper and further transmitting the power through the threshing counter case 4 containing an intermediate transmission mechanism therein to a thresher 5 with a belt therein attached onto an undercarriage 7.
