To easily perform the removal of a used injection needle unit without directly touching by hand by a method wherein a plurality of engaging utensils which are engaged with the upper edge part of a flange of the fitting part of the injector needle unit, and then, pull up a cartridge holder to remove the fitting part of the injection needle unit, are provided.

An annular body 10 of a cartridge holder 1 in which the fitting part 2a of an injection needle unit is fitted, is inserted to a receiving port 5a of an injector needle removing device 5, and the annular body 10 is advanced while warping engaging utensils to the outside by pressing the tilted parts of hook parts of the engaging utensils 6. Then, the annular part 10 has reached to the outside of the tilted parts of the hook parts of the engaging utensils 6, the annular part 10 is further advanced, and when reached the upper part 2d of the flange 2c of the fitting part 2a, the hook parts of the engaging utensils 6 which have been removed from the tilted part return to the inside in an annular space 12 for the engaging utensils, by the elasticity of the engaging utensils 6. Under this state, a force is applied in order to pull out the annular body 10 upward, a small proturding body 1c moves upward as well together with the annular body 10. At this point, the pinching is released, and the fitting part 2a drops in a housing container 9.