The present invention aims to provide an injection needle assembly that reduces force required for an attachment between the injection needle assembly and a drug discharge tube, and that can surely be attached even with weak force without causing a liquid leakage. An injection needle assembly 2 includes: an injection needle 11； a fitting portion 12 which is formed into a cylindrical shape and has one end serving as a fitting opening, the fitting portion having a female taper shape in which an inner diameter of a cylinder hole of the fitting portion becomes smaller toward the inner side from the fitting opening； and a hub 13 provided with the fitting portion 12 for holding the injection needle 11, the injection needle assembly 2 being used in such a manner that the female taper shape of the fitting portion 12 is fitted to a drug discharge tube 22, which has a male taper shape in which an outer diameter of a cylinder becomes smaller toward a tip, from the fitting opening, wherein when the male taper shape of the drug discharge tube 22 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, wherein M >； N.
