PURPOSE: To hold the entire part of an injector hermetic to the outdoor air and to assure the sterile property thereof by providing an outside cylinder which is freely slidably fitted with an injection cylinder and internally houses a double head needle and a blind cylindrical body which is freely attachably and detachably mounted at the rear end thereof and hermetically houses the rear of the injection cylinder.

CONSTITUTION: The injection cylinder 1 which houses a liquid chemical and is mounted with a sealing member 12 pierceable into a front end aperture 11 has a plunger 3 which is freely slidably inserted into the rear end aperture 12 of this injection cylinder 1, a detaining member 4 which freely engageably and disengageably regulates the sliding of the plunger 3 with the injection cylinder 1 and the outside cylinder 5 which is mounted with a sealing member 6 pierceable in the front end aperture 51 and houses the injection cylinder 1 in the rear end aperture 52 freely slidably from the front end thereof. The double head needle 7 which is held and housed approximately along the center line of the outside cylinder 5 and the blind cylindrical body 8 the front end aperture of which is freely attachably and detachably mounted at the rear end of the outside cylinder 5 and which hermetically houses the injection cylinder 1 and the plunger 3 cooperatively with the outside cylinder 5 are provided in this outside cylinder 5.