By a cylinder ampoule (1), comprising a tubular vessel with a membrane (4) sealingly closing one end and a piston (9) closing the other end, liquid stored between said piston (9) and said membrane (4) can be pressed out through an injection needle (7) piercing the membrane (4) when the piston (9) is pressed into the ampoule (1). The tube is made from a plastically deformable material. A pressure foot (10) on which a piston rod (13) is acting abuts the piston (9), carries a spring plate (11) made from a harder material than is the ampoule (1), is mainly perpendicular to the ampoule (1) axis, and has at least one diameter which is larger than the inner diameter of the ampoule (1) so that edges of the plate (11) abutting the inner wall of the ampoule (1) are deflected away from the piston (9) to form an acute angle with said wall. The ampoule (1) has an extension (14) beyond the position of the piston (9) by a full ampoule (1) and forms a part of a pen shaped syringe further comprising a dose setting and injection means co-operating with the piston rod (13).