Abstract: The present invention relates to a maize sheller having at least one drum and counter drum (concave). The counter drum has an adjustable part and a non-adjustable part. The maize sheller according to the invention possesses a regulating mechanism for regulating clearance between the drum and the adjustable part of the counter drum. The use of a counter drum of such a construction economizes a significant amount of metal and enhances the screening capacity and the productivity of the entire device. The regulation of the outlet aperture within a comparatively wide range permits the use of the maize sheller for shelling corn cobs of different sizes and with different moisture content without causing damage to the grain. In case of penetration of foreign matter into the shelling apparatus, the drum and the counter drum are protected against deformation by a safety sector which is automatically opened.