A metering device is able to be fixed to a system for distribution of particles for agricultural machine, comprising a reservoir (30) with a conveyor (20) able to transport the particles of the reservoir towards an outlet orifice. Such a metering device comprises at least one movable flap (51) which is inclined with respect to the vertical, so that the angle (α) formed - between the trap door (s) and a plane of the conveyor is an acute angle, which makes it possible to facilitate their actuating. In addition, in the closed position, a lower end of the trap door (s) is located to the vertical axis of rotation of a drive roller of the conveyor, i.e. perpendicularly to the point where the particles leave the conveyor. This allows a controlled supply of the module of the spreading arranged downstream of the device, with a minimum delay of reaction. This improves the accuracy of dosing.
