When overlapping and joining together end portions of a rubber member, it becomes possible to join them at a joining area smaller than a conventional one by increasing the joining area. There is provided a joining device for overlapping end portions, of a rubber member (tire constituent member) with one upper end portion placing on the other lower end portion and joining the end portions of the rubber member, in which a pressing roll (disk-shaped roll) rotating about an inclined shaft is rolled while being pressed against the overlapped upper end portion of the rubber member, and the upper end portion is extended by a shearing force generated at this time to increase a joining area between the both end portions.