A drive unit for a forming machine, comprising a rotary drive and a knuckle-joint drive for a gear transmission operating a ram, the knuckle-joint drive being operationally connected through a gear transmission to the rotary drive. To improve the drive rigidity as regards a forming machine and to be able to improve the drive-unit design and to relatively easily match the drive unit to the specific requirements of different forming methods, the gear transmission offers a periodically varying transmission ratio, at least two mutually engaging non-circular gears being used of which the pitch curves are designed in such manner that in conjunction with the knuckle-joint drive, and especially in conjunction with a subsequent crank drive, the motions of the ram will be optimally matched thereby to the particular work method.