An apparatus for loading a relatively rigid material in sheets into an operating station of a processing plant, comprises at least a store for storing and feeding the sheets and a loading device. The loading device is provided at least with feed means, disposed downstream of the store with respect to the direction of feed of the sheets, and able to feed the sheets into the operating station. The apparatus also comprises detection means, disposed in correspondence with the feed means, able to detect both the position of the sheets with respect to the feed means, and also the size of the sheets fed. The detection means are also able to vary in a coordinated manner the operating conditions at least of the feed means according to the position and sizes detected.