Apparatus for unwinding cables on seabeds, which comprises: - two movable towers arranged parallel to and spaced from each other and intended to be arranged on a support platform; - two hubs, which are arranged facing each other, are rotatably constrained to the corresponding said movable towers around a first rotation axis, and are susceptible of being mechanically engaged with a reel, which is provided with a drum intended to be arranged coaxially with respect to said first rotation axis and with a cable wound around said drum and organized in at least one row of coils, such coils arranged side-by-side each other along said first rotation axis and comprise a terminal coil from which said cable is susceptible of being unwound from said drum; - movement means mechanically connected to said hubs and adapted to rotate said hubs around said first rotation axis in order to drive said reel to rotate around said first rotation axis so as to at least unwind said cable from said drum at said terminal coil; - a laying tower intended to be fixed on said support platform; - transmission means, which are mounted on said laying tower, are arranged to intercept an unwinding direction substantially orthogonal to the first rotation axis of said hubs and passing between said movable towers, and are susceptible of receiving, in engagement, a section of said cable unwound from said drum and of transmitting the section of said cable downward; said apparatus being characterized in that it also comprises: - a transverse track, which is extended according to a moving direction parallel to said first rotation axis and carries, slidably constrained thereto, said movable towers; - moving means mechanically connected to said movable towers and adapted to move said movable towers along said transverse track according to said moving direction; - position identification means arranged for determining at least one position parameter indicative of the position, along said first rotation axis, of the terminal coil of the cable of said reel; - control means operatively connected to said position identification means and to said moving means and arranged for commanding, as a function of said position parameter, said moving means to move said movable towers along said moving direction, in order to maintain said terminal coil substantially aligned with said unwinding direction; - detection means arranged for measuring the rotation speed of said reel around said first rotation axis and operatively connected to said control means in order to send measurements of said rotation speed to said control means; said control means being arranged for commanding, as a function of said measurements, said movable towers to be moved along said transverse track with an overall linear movement speed proportional to said rotation speed. - two movable towers arranged parallel to and spaced from each other and intended to be arranged on a support platform; - two hubs, which are arranged facing each other, are rotatably constrained to the corresponding said movable towers around a first rotation axis, and are susceptible of being mechanically engaged with a reel, which is provided with a drum intended to be arranged coaxially with respect to said first rotation axis and with a cable wound around said drum and organized in at least one row of coils, such coils arranged side-by-side each other along said first rotation axis and comprise a terminal coil from which said cable is susceptible of being unwound from said drum; - movement means mechanically connected to said hubs and adapted to rotate said hubs around said first rotation axis in order to drive said reel to rotate around said first rotation axis so as to at least unwind said cable from said drum at said terminal coil; - a laying tower intended to be fixed on said support platform; - transmission means, which are mounted on said laying tower, are arranged to intercept an unwinding direction substantially orthogonal to the first rotation axis of said hubs and passing between said movable towers, and are susceptible of receiving, in engagement, a section of said cable unwound from said drum and of transmitting the section of said cable downward; - a transverse track, which is extended according to a moving direction parallel to said first rotation axis and carries, slidably constrained thereto, said movable towers; - moving means mechanically connected to said movable towers and adapted to move said movable towers along said transverse track according to said moving direction; - position identification means arranged for determining at least one position parameter indicative of the position, along said first rotation axis, of the terminal coil of the cable of said reel; - control means operatively connected to said position identification means and to said moving means and arranged for commanding, as a function of said position parameter, said moving means to move said movable towers along said moving direction, in order to maintain said terminal coil substantially aligned with said unwinding direction; - detection means arranged for measuring the rotation speed of said reel around said first rotation axis and operatively connected to said control means in order to send measurements of said rotation speed to said control means;