A flat-article feed device comprising a supply magazine in which flat articles are moved in a stack on edge in a first transfer direction, a separator for separating the leading flat article of the stack from the remainder of the stack and for driving it in a second transfer direction that is substantially perpendicular to the first transfer direction, an unstacker that takes a flat article that is being unstacked and brings it in the second transfer direction to the inlet of a conveyor, and a retainer that exerts a retaining force that opposes movement of the flat article towards the conveyor, the unstacker being offset from the separator by a distance not less than the maximum length of a flat article, and the retainer being provided facing the unstacker. A postal sorting machine including such a feed device.