Spinal fixation system

PURPOSE: Provided is a fixing apparatus for the spine which securely fastens a rod mounted on a head and stably maintains the fastened state, and by which the fixing operation is performed readily and conveniently. CONSTITUTION: The fixing apparatus for the spine includes a head having screw threads on the inner surface thereof, in which the inner surface with the screw threads has a shape such that the direction to which the peaks of the screw threads are headed are inclined to form an acute angle with an opposite direction to the direction along which the screw proceeds when it rotates; a fastening part extending from the head to be screw-bound to the bone; a rod to be mounted on the inside of the head; and a screw bound with the screw threads of the head to fix the rod.