An apparatus for advancing and sorting objects in respect of their size comprises a plurality of juxtaposed, endless conveyor belts (10) and gaps (9) between adjacent conveyor belts, each conveyor belt consisting of a plurality of hinged segments or chain elements (11) and a system (23, 24) for driving the conveyor belts. To obtain an advancement of the objects which is as lenient and noiseless as possible, the conveyor belts (10) are combined with and guided by guide rails (30) which extend substantially along the entire run of the belt which advances the objects. The guide rails are so arranged and designed, that the gap (9) between mutually adjacent conveyor belts continually increases along at least the major part of said belt run. Each belt segment (11) comprises a bridge portion which as seen in a cross section forms an inverted V and the ends of which are moveable with respect to each other in a direction which is substantially perpendicular to the advancement direction of the belt and are each connected to an individual base portion (13) which embraces and is guided by the two longitudinal edges of the guide rail (30).