Abstract: A coupling system between an operating machine and a planetary gearbox. The coupling system comprising an axially rotatable machine shaft of an operating machine; and a slow gearbox shaft of a planetary gearbox connectable integrally in rotation with the machine shaft in an operational configuration. The machine shaft and the slow gearbox shaft comprise a first coupling portion and a second coupling portion, respectively, substantially truncated cone-shaped and complementary to each other, the first coupling portion and the second coupling portion being conically coupled to each other in the operational configuration.