The present disclosure relates to a medicament delivery device (1) comprising a body (11), an axially biased plunger rod (15) provided with a first external thread (15a), an activation member (5) arranged to activate the plunger rod (15), a tubular medicament scale member (21) receiving the activation member (5), which tubular medicament scale member (21) is rotatable relative to the body (11) and provided with a visual medicament dose scale (7), a stop nut (23) which receives the plunger rod (15) and which stop nut (25) is provided with an internal thread engaging with the first external thread (15a) of the plunger rod (15), and a gear train arrangement (37) arranged to, in a decoupled state decouple the stop nut (23) from the tubular medicament scale member (21), and in a coupled state couple the stop nut (23) to the tubular medicament scale member (21) for transferring rotational motion of the stop nut (23) to the tubular medicament scale member (21), in order to convey a measure of axial movement of the plunger rod (15) to the tubular medicament scale member (21), thereby providing an indication, on the visual medicament dose scale (7), of an amount of expelled medicament.La présente invention concerne un dispositif d'administration de médicament (1) comprenant un corps (11), une tige de piston (15) axialement sollicitée pourvue d'un premier filetage externe (15a), un élément d'activation (5) agencé pour activer la tige de piston (15), un élément d'indexation de médicament tubulaire (21) recevant l'élément d'activation (5), lequel élément d'indexation de médicament tubulaire (21) peut tourner par rapport au corps (11) et est pourvu d'une indexation de dose de médicament visuelle (7), un écrou d'arrêt (25) qui reçoit la tige de piston (15), cet écrou d'arrêt (25) étant pourvu d'un filetage interne se couplant au premier filetage externe (15a) de la tige de piston (15), et un agencement de train d'engrenages (37) agencé pour, dans un état découplé, découpler l'écr
