A connecting device for flexible pipes, comprising: - a supporting body, having at least one tubular portion protruding form a first end of the body and which may be inserted in a relative flexible pipe, wherein the tubular portion of the supporting body has a plurality of zones consecutive to each other and each having a different transversal cross-sectional dimension; the zones increasing in size starting from an end of the tubular portion; - a seal ring, extending axially between a first, in contact with said first end, and a second edge, positioned around the end of the tubular portion of the supporting body and switchable between an engaging position wherein it retains the flexible pipe on the tubular portion and a releasing position wherein it disengages the flexible pipe; said ring comprising at least one annular rib, concentric with the longitudinal extension of the tubular portion and protruding from the inner surface of the ring; - means of moving the seal ring for switching the ring between the engaging position and the releasing position; wherein the tubular portion of the supporting body comprises at least one protruding element, extending from the outer surface of the tubular portion along the entire transversal extension of the portion; the protruding element being interposed between two adjacent zones of the tubular portion having a different transversal cross-sectional dimensions; wherein an outer surface of the ring has a first portion and a second portion arranged one after another along an axial extension of the ring and connected at a relative intermediate zone of the selfsame outer surface; the first portion having a truncated cone shape, extending away from the second edge with increasing cross-section and the second portion extending between the intermediate zone and the first edge forming a substantially cylindrical profile; characterized in that the seal ring comprises at least one annular rib for each zone of the tubular portion, wherein said at least one rib faces a relative zone of the tubular portion so that, when the seal ring is in the engaging position, the at least one rib facing the zone alternate with each other, along the longitudinal axis of the connecting device, with the protruding element. - a supporting body, having at least one tubular portion protruding form a first end of the body and which may be inserted in a relative flexible pipe, wherein the tubular portion of the supporting body has a plurality of zones consecutive to each other and each having a different transversal cross-sectional dimension; the zones increasing in size starting from an end of the tubular portion; - a seal ring, extending axially between a first, in contact with said first end, and a second edge, positioned around the end of the tubular portion of the supporting body and switchable between an engaging position wherein it retains the flexible pipe on the tubular portion and a releasing position wherein it disengages the flexible pipe; said ring comprising at least one annular rib, concentric with the longitudinal extension of the tubular portion and protruding from the inner surface of the ring; - means of moving the seal ring for switching the ring between the engaging position and the releasing position;