In order to minimize the loss of production of a crushing plant, particularly a cement crushing plant and optimize on the gear side the availability of the roller mill, according to the invention a replacement gear is provided alongside the operating mill gear. The mill gear and replacement gear are located on at least one base plate and preferably together with a drive motor for the mill gear and a second motor for the replacement gear, as well as with a lubricating system located between the mill gear and the replacement gear, are preassembled on the base plate. The base plate is horizontally adjustably guided on the mill foundation. If the mill gear fails the base plate with the units mounted thereon can be adjusted in such a way that the replacement gear is positioned below the crushing pan in the place of the mill gear.