A device for applying self-adhesive labels on the walls of containers, in particular bottles, the device being operatively connectable to an operating machine of the type with a rotary carrousel on which, in practice, the containers are positioned; comprising: a supporting body extending from a first end connected to a basic mechanical unit to a second end which is close to the rotary carrousel; at least one operating head connected to the supporting body at the second end and which can operate on a container positioned on the carrousel, in such a way that it is synchronised with the movement of the carrousel; the operating head comprising an application portion which, in practice, directly interacts with the walls of a container; label feed means for feeding a web comprising labels to bring at least one label at a time to the operating head; there being the possibility of synchronising the label feed means with the movement of the carrousel; the label feed means comprising a feeding roller for storing the web to be used, and a receiving roller for receiving the web once the labels have been removed from it; the web following a feed path from the feeding roller to the receiving roller; guide means for guiding the web from the feeding roller to the operating head and from the operating head to the receiving roller; wherein the application portion of the operating head can move along an arc of a circle which at a tangent point is at a tangent at least to a wall of a container positioned on the carrousel and at the operating head; characterised in that the guide means comprise an inversion plate positioned along the web feed path and mounted on the operating head; the inversion plate comprising an away surface, a return surface which is substantially parallel with and opposite the away surface, and a detaching edge between the two surfaces; the web releasing the labels at the detaching edge as it passes from the away surface to the return surface. a supporting body extending from a first end connected to a basic mechanical unit to a second end which is close to the rotary carrousel; at least one operating head connected to the supporting body at the second end and which can operate on a container positioned on the carrousel, in such a way that it is synchronised with the movement of the carrousel; the operating head comprising an application portion which, in practice, directly interacts with the walls of a container; label feed means for feeding a web comprising labels to bring at least one label at a time to the operating head; there being the possibility of synchronising the label feed means with the movement of the carrousel; the label feed means comprising a feeding roller for storing the web to be used, and a receiving roller for receiving the web once the labels have been removed from it; the web following a feed path from the feeding roller to the receiving roller; guide means for guiding the web from the feeding roller to the operating head and from the operating head to the receiving roller; wherein the application portion of the operating head can move along an arc of a circle which at a tangent point is at a tangent at least to a wall of a container positioned on the carrousel and at the operating head; characterised in that the guide means comprise an inversion plate positioned along the web feed path and mounted on the operating head; the inversion plate comprising an away surface, a return surface which is substantially parallel with and opposite the away surface, and a detaching edge between the two surfaces; the web releasing the labels at the detaching edge as it passes from the away surface to the return surface.