Device for weighing flat objects in motion comprising a conveyor (12) with drive rollers (22A, 22B) for conveying the flat objects along a transport path (14), a weighing plate (16) facing said transport path and comprising a set of free rollers (160) for receiving the flat objects, and a weighing sensor (18) attached to the weighing plate for measuring the weight of the flat objects during their passage between the conveyor and the weighing plate, wherein the weighing sensor is arranged above the transport path and the conveyor is adapted to move vertically in order to press the flat objects in motion against the weighing plate.