PURPOSE: To make it possible to install panels from indoor side by adopting a joint structure which makes a cut end surface of the panels installed in an under edge of a waterproof surface of a joiner to stick to a gasket and fixes a fixing piece with the rear side of the panels.

CONSTITUTION: A plurality of projected strips protruding longitudinally are formed on the way of a fixing piece 1 designed to fix a joiner A. On the other hand, an elastic gasket C is extruded in one piece and molded in the case when the joiner A is extrusion-molded. The gasket C of the joiner A is inserted into a space 5 so that it may stick to the surface of a decorated part 2 of a cut end surface D3 of a fixed panel D1 while one party of the fixing piece 1 is fixed with the rear side of a panel D1 with a fixture β as well. Then, the end of an adjacent panel D2 is inserted into the space 5, thereby fixing the gasket C from the rear side under compression and deformation.