An unwinder for unwinding reels of paper includes a supporting structure partially closed and defining an internal space suitable for unwinding at least one reel; the supporting structure includes: a first lateral support; a second lateral support spaced from the first support; a crosspiece interposed above between the first and the second support defining with the first support and second support the partially closed structure; the unwinder further includes: a first axial unwinding system placed at the first support and configured to axially unwind a first reel; a second axial unwinding system placed at the second support and configured to unwind a second reel; a joining device placed at the crosspiece and configured to make a joint between a first ply belonging to the first reel and a second ply belonging to the second reel to perform a reel exchange.