A device for stretching a thermoplastic film simultaneously in the longitudinal direction and the transverse direction is provided. The device includes, on each side of the film (F) to be stretched, grasping members for grasping a lateral edge of the film (F), and guide members; first and second guide rails (R1, R2), on which the members and are respectively able to move; first connecting rods connecting the grasping members and the guide members. In an embodiment, each guide member is connected to a single grasping member by one or several of said first connecting rods, and is connected to a first longitudinal adjusting member by one or several second connecting rods connected to the first longitudinal adjusting member; and the device includes adjusting means for adjusting the position and orientation of said first longitudinal adjusting member relative to said first and second guide rail (R1, R2).