An injection needle assembly includes an injection needle, a fitting portion, and a hub. The fitting portion is formed into a cylindrical shape and has one end serving as a fitting opening. The fitting portion includes a female taper shape in which an inner diameter of a cylindrical hole of the fitting portion becomes smaller toward an inner side. The hub includes the fitting portion for holding the injection needle. The injection needle assembly is used such that the female taper shape of the fitting portion is fitted to a drug discharge tube, which has a male taper shape in which an outer diameter of a cylinder becomes smaller toward a tip. When the male taper shape of the drug discharge tube has a taper ratio of N/100, the female taper shape of the fitting portion 12 is formed to have a taper ratio of M/100, where M>；N.
