The utility model belongs to the field of medical instruments, and particularly relates to an injector, comprising a needle tube and a push rod; a propelling sleeve with internal threads is arranged at the rear end of the needle tube; and the push rod has external threads matched with the internal threads of the propelling sleeve. The propelling sleeve is arranged at the rear end of the needle tube, the push rod can be rotated by small force as the propelling sleeve and the push rod are in thread connection, and the rotary push rod moves along the axis of the push rod relative to the propelling sleeve, thus pushing medicine to realize the injection process and being convenient to use.