This tissue-joining member comprises non-crosslinked fibrous collagen. A laminate body comprises: a support; a joining member that is layered on one surface of the support; and a first adhesive layer that is layered on said one surface of the support in a region on which the joining member is not layered. The method for using the joining member or the laminate body comprises: a heating step in which the joining member or the laminate body is heated to less than 60° C. and greater than body temperature after having being layered on the tissue; and a cooling step in which the heated joining member or laminate body is cooled to body temperature or lower. A treatment system comprises a heating unit and the joining member or the laminate body.