PROBLEM TO BE SOLVED: To provide a guide instrument for bone surgery that facilitates forming two cut surfaces being parallel, while ensuring an area of a cut surface, and a bone fixator capable of sufficiently fixing a separated bone while being a simple and narrow shape.SOLUTION: A guide instrument for bone surgery includes: a first guide part 4 having a first guide surface defining a cut surface and a first guide hole positioning the first guide surface to a first bone portion a second guide part 5 having a second guide surface for defining the cut surface while being spaced apart from the first guide surface and opposed by a resection portion of a bone, and a second guide hole for positioning the second guide surface in the second bone portion and a guide shaft 10 for supporting the first guide part and the second guide part relatively movably in the longitudinal direction by maintaining the parallel between the first guide surface and the second guide surface. When connecting the first bone portion with the second bone portion of the bone after the resection, the first guide hole is aligned with the second guide hole, and the distance of the hole formed in the bone is maintained constantly.
