A joining apparatus for supporting strips (2a, 2b) of adhesive labels conveyed by a labelling machine along a conveying direction between a respective starting reel (4a, 4b) and a collection reel, said joining apparatus comprising two modules (5a, 5b) that can be moved with respect to one other between a distanced configuration and a neared configuration and each of which being configured to convey a respective supporting strip (2a, 2b), each of said modules (5a, 5b) comprising: - at least one conveying element of the respective supporting strip (2a, 2b); - at least one cutting element (7a, 7b) arranged along said conveying direction and configured to cut a respective supporting strip (2a, 2b) at a joining zone (10a, 10b) of the same supporting strip (2a, 2b); - at least one joining element (8a, 8b) arranged along said conveying direction and that can be configured in a first operating position, wherein it keeps in position a joining zone (10a, 10b) of the respective supporting strip (2a, 2b) and/or a fixing element, and in a second operating position wherein it abuts against the joining element (8a, 8b) of the other module (5a, 5b) so as to join a first joining zone of a first supporting strip to a second joining zone of a second supporting strip; - at least one locking element (9a, 9b) arranged along said conveying direction and that can be configured between an active position, wherein it prevents the conveying of the supporting strip (2a, 2b), and a passive position, wherein it allows the conveying of the supporting strip (2a, 2b); characterised in that said at least one joining element (8a, 8b) of at least one of said two modules (5a, 5b) is configured to be removable from the respective module (5a, 5b) so as to leave free, in a removed configuration, an access compartment extending through said module (5a, 5b) and transversally to the conveying direction at the modules (5a, 5b) to allow the introduction of the fixing element also when said two modules (5a, 5b) are in the neared configuration so as to apply said fixing element to a rear surface free from adhesive labels of the joining zone (10a, 10b) of a supporting strip (2a, 2b). - at least one conveying element of the respective supporting strip (2a, 2b); - at least one cutting element (7a, 7b) arranged along said conveying direction and configured to cut a respective supporting strip (2a, 2b) at a joining zone (10a, 10b) of the same supporting strip (2a, 2b); - at least one joining element (8a, 8b) arranged along said conveying direction and that can be configured in a first operating position, wherein it keeps in position a joining zone (10a, 10b) of the respective supporting strip (2a, 2b) and/or a fixing element, and in a second operating position wherein it abuts against the joining element (8a, 8b) of the other module (5a, 5b) so as to join a first joining zone of a first supporting strip to a second joining zone of a second supporting strip; - at least one locking element (9a, 9b) arranged along said conveying direction and that can be configured between an active position, wherein it prevents the conveying of the supporting strip (2a, 2b), and a passive position, wherein it allows the conveying of the supporting strip (2a, 2b);