A crank drive system (10) of a shaft (11) of a microtome (1) encompasses a first and a second shaft (11, 12). The first shaft (11) is rotatable with a crank (13) and comprises a first transfer gear (14). The second shaft (12) comprises a second transfer gear (15). A rotation of the first shaft (11) is transferable from the first transfer gear (14) to the second transfer gear (15) to cause the second shaft (12) to rotate. To make possible, with a microtome (1), an advance or a lowering of the specimen (2) in two respective oppositely directed rotation directions with the same crank drive system (10), the crank drive system (10) is characterized in that a third transfer gear (16) is provided. The first transfer gear (14) is selectably engageable with the second transfer gear (15) or with the third transfer gear (16) so that as a result, while the rotation direction of the second shaft (12) is maintained, the rotation direction of the first shaft (11) is reversible.