An injection needle assembly includes a needle tube, a needle hub holding the needle tube, a protector, a biasing member, a sliding groove, and a sliding protrusion. The protector is movable between a first position at which the needle tip of the needle tube is covered and a second position at which the needle tip of the needle tube is exposed. The sliding groove is located at one of the needle hub or the protector. The sliding protrusion is located at the other of the needle hub or the protector and is slidably disposed in the sliding groove,
