A device for joining webs with self-adhesive labels to be supplied to a labelling machine, comprising: a supporting structure; at least two supports each for supporting a reel of web with self-adhesive labels fixed on one side of it, the supports being rotatably mounted or mountable on the supporting structure, one at a first position and one at a second position; first guide means defining a main feed path for a first web which in use extends from a first reel mounted on the support positioned in the first position, to an outfeed section where, in use, the web is supplied to the labelling machine, an operating zone being defined along the feed path; second guide means defining a secondary feed path for a second web which in use extends from a second reel mounted on the support positioned in the second position, to the operating zone; and joining means mounted on the supporting structure at the operating zone, for in use joining a starting end of the second web to a final end of the first web, by pressing the final end of the first web against an adhesive element fixed to the starting end of the second web; the joining means in turn comprising: a web retaining element mounted at an end portion of the secondary feed path for, in use, selectively retaining the starting end of the second web in the absence of stresses or allowing uncoupling of the starting end of the second web following a pulling action applied on it after at least partial joining of the first web and the second web; and a pressure element positioned in said operating zone on the opposite side of the main feed path to the retaining element; at least one of either the retaining element or the pressure element being movable relative to the other, between a non-operating position in which they are at a distance from one another and, in use, the first web can freely run between them, and an operating position in which the pressure element is pressed onto the retaining element for, in use, pressing the final end of the first web onto the adhesive element fixed to the starting end of the second web which is retained by the retaining element; characterised in that the joining means further comprise: at least one cutting element, mounted along the main feed path upstream of the pressure element, and movable between a non-interference position in which in use it does not interfere with the first web being fed along the main feed path, and a cutting position in which it interferes with main feed path for cutting the first web; movement means for moving the cutting element from the non-interference position to the cutting position; and means for controlled feeding of the first web along the main feed path, which are operatively associated with the movement means for causing controlled feeding of the first web in the operating zone during the movement of the cutting element towards the cutting position. a supporting structure; at least two supports each for supporting a reel of web with self-adhesive labels fixed on one side of it, the supports being rotatably mounted or mountable on the supporting structure, one at a first position and one at a second position; first guide means defining a main feed path for a first web which in use extends from a first reel mounted on the support positioned in the first position, to an outfeed section where, in use, the web is supplied to the labelling machine, an operating zone being defined along the feed path; second guide means defining a secondary feed path for a second web which in use extends from a second reel mounted on the support positioned in the second position, to the operating zone; and joining means mounted on the supporting structure at the operating zone, for in use joining a starting end of the second web to a final end of the first web, by pressing the final end of the first web against an adhesive element fixed to the starting end of the second web; a web retaining element mounted at an end portion of the secondary feed path for, in use, selectively retaining the starting end of the second web in the absence of stresses or allowing uncoupling of the starting end of the second web following a pulling action applied on it after at least partial joining of the first web and the second web; and a pressure element positioned in said operating zone on the opposite side of the main feed path to the retaining element; at least one of either the retaining element or the pressure element being movable relative to the other, between a non-operating position in which they are at a distance from one another and, in use, the first web can freely run between them, and an operating position in which the pressure element is pressed onto the retaining element for, in use, pressing the final end of the first web onto the adhesive element fixed to the starting end of the second web which is retained by the retaining element; at least one cutting element, mounted along the main feed path upstream of the pressure element, and movable between a non-interference position in which in use it does not interfere with the first web being fed along the main feed path, and a cutting position in which it interferes with main feed path for cutting the first web; movement means for moving the cutting element from the non-interference position to the cutting position; and means for controlled feeding of the first web along the main feed path, which are operatively associated with the movement means for causing controlled feeding of the first web in the operating zone during the movement of the cutting element towards the cutting position.