Abstract: It is provided for a reclining device for chairs and the chair with said reclining device, comprising an elastic element with linear strain (8) having a first end (8a) abutting against the primary body (2) of a chair, and a half-shell element (12) adapted to house at least a portion of the elastic element (8) starting from a second end (8b) of the latter, said half-shell element (12) having two abutment portions (12b) for a pair of pushing extensions (13) integral with the support element (4) of the reclining back.