A device for administering a fluid product, such as an industrial or a medical compound comprising: -a reservoir (18) in which a plunger (15) is axially movable; -an axially movable rod (16) on which a ferromagnetic rod connector (12) is attached, said ferromagnetic rod connector (12) being adapted for sliding cooperation within said reservoir (18); -wherein detachable mechanical connection between the plunger (15) and the ferromagnetic rod connector (12) is provided with a ferromagnetic plunger connector (13) attached to said plunger and a magnet (11), arranged for magnetic cooperation with said ferromagnetic connectors (12, 3) to provided a mechanical connection between the ferromagnetic connectors.