Apparatus for unwinding flexible cables on seabeds, which comprises: - two first towers arranged parallel to and spaced from each other; - two hubs, which are arranged facing each other, are susceptible of being associated with the corresponding said first towers and are susceptible of being mechanically engaged with corresponding ends of a drum (14', 16', 21') of a reel (14, 16, 21) in order to rotatably support said reel (14, 16, 21); - movement means (11, 12) arranged for moving each said hub along the corresponding said first tower; each said first tower comprising a first guide seat extended along a first substantially vertical movement direction (Y'); said apparatus being characterized in that it also comprises: - two second towers arranged parallel to and spaced from each other, each of such second towers provided with a second guide seat extended along a second movement direction (Y") parallel to said first movement direction (Y'); - two hub-holder groups, each of which is slidably constrained to the second guide seat of the corresponding said second tower and carries, rotatably mounted thereon, the corresponding said hub; - translation means, which are arranged for moving each said second tower between a first operating configuration, in which said second tower is slidably constrained in the first guide seat of said corresponding first tower, and a second operating configuration, in which said second tower is arranged outside the first guide seat of said corresponding first tower; said movement means (11, 12) comprising: - a first movement system mechanically connected to said second towers and arranged for moving each said second tower, arranged in said first operating configuration, in the corresponding said first guide seat along said first movement direction (Y'); - a second movement system mechanically connected to said hub-holder groups and arranged for moving each said hub-holder group in the corresponding said second guide seat along said second movement direction (Y"). - two first towers arranged parallel to and spaced from each other; - two hubs, which are arranged facing each other, are susceptible of being associated with the corresponding said first towers and are susceptible of being mechanically engaged with corresponding ends of a drum (14', 16', 21') of a reel (14, 16, 21) in order to rotatably support said reel (14, 16, 21); - movement means (11, 12) arranged for moving each said hub along the corresponding said first tower; - two second towers arranged parallel to and spaced from each other, each of such second towers provided with a second guide seat extended along a second movement direction (Y") parallel to said first movement direction (Y'); - two hub-holder groups, each of which is slidably constrained to the second guide seat of the corresponding said second tower and carries, rotatably mounted thereon, the corresponding said hub; - translation means, which are arranged for moving each said second tower between a first operating configuration, in which said second tower is slidably constrained in the first guide seat of said corresponding first tower, and a second operating configuration, in which said second tower is arranged outside the first guide seat of said corresponding first tower; - a first movement system mechanically connected to said second towers and arranged for moving each said second tower, arranged in said first operating configuration, in the corresponding said first guide seat along said first movement direction (Y'); - a second movement system mechanically connected to said hub-holder groups and arranged for moving each said hub-holder group in the corresponding said second guide seat along said second movement direction (Y").