A hydraulically operated rotary pipe bending machine has a box (1) from which superiorly protrude a die shaft (2) that is rigidly connected to a die and integral with a die gear (29) being driven by an actuator (30) through a hydraulic circuit and being stopped by a limit switch device (8), and a counter-die unit (3) driven by a handwheel (4) in order to place an elongated piece to be bent against said die. The actuator (30) has a single-acting cylinder, having a piston (31) holding a rack rod (30a) engaging said die gear (29), the piston (31) being opposed in its travel by a return spring (33). The limit switch device (8) has an angularly graduated disc (10) mounted, manually adjustable, on the die shaft (2) and provided with a cam (16) designed to control said limit switch (17) of the hydraulic circuit.