Device for the formation of a package (4) of envelopes (1), vertically juxtaposed and stacked, said package comprising a front cover (2) and a back cover (2), both of a size equivalent to the size of the envelopes to be packed, and at least one wrapping strip (3) holding both covers and the envelopes included in the package, said covers presenting, in their upper and lower edges, homologous attaching means (21, 22) coupled with tongue and groove in the stacking of the packages and the wrapping strip or strips being placed in a vertical plane that holds the upper and lower edges of the envelopes between the front and back covers.