A pipe bending apparatus with hydraulic transmission, operable with one hand, of the type comprising a cylinder (5,8,50,6) in which there is movable in both directions a die-carrying rod (1), comprises, fixed in correspondence with that (3) of its ends located within the cylinder, a seal element (4) defining together with portions of the walls of said cylinder a first and a second chamber (43,52) of volume variable in relation to the movements of said rod, said chambers being connected via conduits (21,36,56,53A,53B) and at least one intermediate chamber (23) to a reservoir (11) for a fluid. The intermediate chamber (22,23,24) comprises a hydraulic pump operable by one hand, and unidirectional valve means (22,24). The reservoir (11) comprises an at least partly deformable sealing wall (12).