Abstract: This invention relates to an injector with a cartridge for a liquid medicine, which is suitable as a throwaway type or a re-use type, and especially displays remarkable effects at urgent occasions. This injector substantially comprises an injector tube housing a cartridge into a body thereof and a cylinder slidably supporting a piston such that it is not removed therefrom at its end portion and in the injector tube by its front half part. Further, the cartridge is equipped with a concave on its bottom and the piston is equipped with a convex on its head for engaging means. The needle portion comprises an injecting needle and a hollow needle inwardly extending from the needle. If the needle portion is urged while it is fitted to the injector tube, the hollow needle pierces the cartridge and reaches the liquid medicine in the cartridge. The cylinder is defined with a stopper at its circumferential edge to restrain the piston with respect to the cylinder.