A rotary device for sealing a continuous web, preferably for making absorbent articles or for making bags for containing liquid or solid products, comprising an element rotating about its own axis of rotation, one or more elements for supporting a continuous web supported by the rotary element and a plurality of units for welding the continuous web supported by the rotary element; each welding unit is configured to pass from a non-operating position to an operating position and vice versa; each welding unit comprises a respective welding tip and a respective anvil element which is movable relative to the welding tip; each welding unit comprises respective first movement means configured to drive the anvil element in rotation relative to the welding tip from an initial position, where the anvil element is angularly spaced from the welding tip, to a final position, and vice versa; at the final position, the surface of the welding tip and the surface of the anvil element are parallel to each other and the axis at right angles to said surface of the welding tip and the axis at right angles to the surface of the anvil element are aligned along a same axis of alignment; each welding unit comprises second movement means for moving the anvil element relative to the welding tip from a starting position, where the surface of the welding tip and the surface of the anvil element are parallel and aligned with each other along a same axis of alignment, to an arrival position, where the contact surface of the anvil element and the contact surface of the welding tip contact a respective portion of continuous web in a respective zone interposed between them, and vice versa; first drive means configured to drive the first movement means to cause the anvil element to pass from the initial position to the final position and vice versa; second drive means configured to drive the second movement means to cause the passage from the starting position to the arrival position, and vice versa; the first drive means and the second drive means being configured to vary the relative positioning of the welding tip relative to the axis of rotation of the rotary element; characterised in that the first drive means comprise a rod-shaped element and at least one element for transmitting motion to the first movement means; the motion transmission element is slidably constrained to the rod-shaped element to translate along the rod-shaped element and vary its relative position along the rod-shaped element. each welding unit is configured to pass from a non-operating position to an operating position and vice versa; each welding unit comprises a respective welding tip and a respective anvil element which is movable relative to the welding tip; each welding unit comprises respective first movement means configured to drive the anvil element in rotation relative to the welding tip from an initial position, where the anvil element is angularly spaced from the welding tip, to a final position, and vice versa; at the final position, the surface of the welding tip and the surface of the anvil element are parallel to each other and the axis at right angles to said surface of the welding tip and the axis at right angles to the surface of the anvil element are aligned along a same axis of alignment; each welding unit comprises second movement means for moving the anvil element relative to the welding tip from a starting position, where the surface of the welding tip and the surface of the anvil element are parallel and aligned with each other along a same axis of alignment, to an arrival position, where the contact surface of the anvil element and the contact surface of the welding tip contact a respective portion of continuous web in a respective zone interposed between them, and vice versa; first drive means configured to drive the first movement means to cause the anvil element to pass from the initial position to the final position and vice versa; second drive means configured to drive the second movement means to cause the passage from the starting position to the arrival position, and vice versa; the first drive means and the second drive means being configured to vary the relative positioning of the welding tip relative to the axis of rotation of the rotary element; characterised in that the first drive means comprise a rod-shaped element and at least one element for transmitting motion to the first movement means; the motion transmission element is slidably constrained to the rod-shaped element to translate along the rod-shaped element and vary its relative position along the rod-shaped element.