Abstract: The device concerns a driving gear for Convertible public transportation seats with variable spacing (2a, 2b, 2c) along a dimensional axis (3), the seats (2a, 2b, 2c) being mounted on a structure (4) with several adjacent seats (2a, 2b, 2c), with each of them separated from the next by a space between frames (5) and sliding on the structure (4) along the dimensional axis (3). A driving gear comprises a worm (6) whose axis (7) is parallel to the dimensional axis (3) and which is coupled with at least one nut (8) attached to the seat (2a, 2b, 2c) to be driven, in such a way that when the worm (6) is forced to rotate in one direction the seat (2a, 2b, 2c) is driven from one extreme position to another and when the worm (6) is forced to rotate in the other direction the seat (2a, 2b, 2c) is driven to move in the opposite direction.