The rotation device includes means for locking the seat in extreme angular positions, comprising a movable abutment carried by the seat, and interacting with a complimentary fixed abutment when the seat is in one of its extreme angular positions. The movable abutment may be moved between a locked position in which it abuts the fixed abutment, and an unlocked position in which it is above the fixed abutment. The device has a means for unlocking the seat, wherein it comprises at least one pneumatic control member and pneumatic means for driving the movable abutment from its locked position to its unlocked position when the control member is actuated.