Abstract: This invention relates to apparatus used in supporting safety rails and discloses a system in which a safety rail post support and security device is used in pairs or greater multiples to hold pieces of a safety rail at the edge of an elevated surface and is speedily attached to or detached from the three commonly found roof edge structures, that is, roofs that are flat right up to the edge, roofs that have a very low ledge or flashing around the perimeter, and roofs that have a parapet along the edge. Previous systems rely on cantilever weights positioned well in from the edge of the roof, interfering with the work to be done there. The post support and security device has a junction piece comprising four intersecting extruded stabilizer bars perpendicular to each other in one plane and a fifth bar protruding from that plane at ninety degrees. An upright post fits into one of the bars after the junction piece is bolted to a roof or to a wall abutting the edge of a roof, or is clamped to a parapet.