PROBLEM TO BE SOLVED: To provide a spacer which invites no large scale of a spacer and which can be strongly fastened when set in a gap.SOLUTION: The spacer 1 is used by being inserted in a gap to expand the spinal canal 140. The spacer has a body part 2 which includes: a first face (front face) 11 that is inserted in a gap and situated on the spinal canal side, in a state inserted in a gap； a second face (rear face) 12 that is situated opposite to the first face 11； and a third face 13 and a fourth face 14 (a pair of abutting faces) that come in contact with cut end parts 120a, 120b of the vertebral arch or the spinous process respectively. Also, the body part 2 has a hollow and bone storing storage part 39 which is composed of an opening part 31 that opens in the second face 12 and an opening part 32 that opens in the third face 13 and the fourth face 14. The opening part 31, the storage part 39 and the opening part 32 function as insertion holes for fastening the spacer 1 in the gap by inserting a screw 4.SELECTED DRAWING: Figure 5
