Abstract: The present invention relates to a spinal fusion cage which is inserted between vertebral bodies in a state where the cage has the lowest height and is height-adjustable in the inserted state, thus making it possible to replace cages having heights in a certain range by a single cage. Therefore, manufacturers can reduce product groups that need to be produced and can also reduce product stock. Further, in contrast to the conventional cages having predetermined heights at regular intervals, the height of the inventive cage can be linearly adjusted according to the distance between the vertebral bodies of a patient, and thus a surgery for the patient can be performed using the cage adjusted to an optimum height according to the patient's condition.