A safety needle assembly includes a hub including a proximal end connected to a syringe and a distal end, a cannula having a thickness of 18 to 24 gauge and a length between the hub and a distal end of 8 to 22 mm, and a sheath which houses the cannula. The sheath includes a projecting stopper for restricting movement, toward a distal end of the sheath, of a finger of a user pushing the sheath for housing the cannula into the opening of the sheath. The sheath includes a rib which guides the cannula introduced into the opening and a guide rib which has a locking protrusion for locking the cannula with an angle of 0° or more with respect to a housing direction of the cannula after the cannula has passed the locking protrusion.
