A hemming device is provided including a lower die, an exterior panel disposed at the lower die, and an interior panel disposed on the exterior panel and bending an edge flange portion of the exterior panel to be adjacent to the interior panel. The hemming device further includes a hemming multi-cam formed with a first hemming surface primarily bending the flange portion of the exterior panel and formed with a second hemming surface secondarily bending the flange part at one side of the first hemming surface. Additionally, a seesaw cam having a tip end portion formed with a cam tip end surface bonds the interior panel to the exterior panel and bends the flange portion secondarily bent by the second hemming surface to be adjacent to the exterior surface of the interior panel.