Fiber stretching device for roving frames, which comprises: at least a first cylinder (1) and a second cylinder (2), both motorized, disposed in parallel in fixed positions; and a plurality of pressing arms (3), disposed in perpendicular to the motorized cylinders (1, 2) and provided with first rollers (31) and second rollers (32), both freely rotating, and upper bags (4) which embrace the corresponding freely rotating second roller (32) and support means (41) of said upper bags. The upper bags (4) press the fibers to stretch (F) directly against support zones (21) of the second motorized cylinder (2), and wherein said device does not have lower bags for the support of the upper bags (4), nor of a static track for the support of said lower bags.