Abstract: A device forms metallic cages for structures made of reinforced concrete, the metallic cages providing longitudinal rods associated with transverse stirrups, the transverse stirrups having an at least partly closed shape and being distanced lengthwise. The device includes a supporting frame, and a plurality of housing seatings arranged in a longitudinal line on the supporting frame at least according to a desired interaxis (“i”) or a multiple of the interaxis (“i”), each of the housing seatings cooperating with a relative means to position and retain the stirrups defining their erect position on a substantially vertical plane. A plurality of transverse arms to support the longitudinal rods lie separated from each other on a horizontal plane, the transverse arms being interposed between the housing seatings. Means are provided for relative displacement in height between the transverse arms and the means to position and retain the stirrups.