A leg and foot support structure applied to tiltable armchairs, comprised of a quadrangular rigid structure, said quadrangular rigid structure being lifted by means of feet; a pivotable quadrangular articulated frame for supporting the feet that is assembled on the front half and within said rigid structure; moving parts of said structure being operated by driving assemblies comprised of articulated arms connected and actuated simultaneously by a driving unit. An inner sliding frame composed of two quadrangular structures that slide over each other through articulated arms pivoted to the respective structures and to a rigid articulated frame that is angularly moved in order to be underneath a seat structure; said quadrangular structures start their relative slippage only after the articulated rigid frame reaches an end of its angular displacement.