To certainly hold mutual bones to a long-term joined state at a bone fracture place.

The bone joining instrument is constituted of a joining bolt 12, which is embedded in a bone over the range from a diaphysis part A to a bone head part B so as to straddle the bone fracture place and has a screw part 22 formed to the leading end thereof to be threaded with the bone head part B, and a support plate 13 fixed to the diaphysis part A to support the rear end of the joining bolt 12. A hollow hole 21 piercing through the joining bolt 12 and the through-holes 23 communicating with the hollow hole 21 on the peripheral surface on the leading end side of the joining bolt 12 are formed to the joining bolt 12. Bone cement is injected in the joining bolt 1 from the rear end thereof to the hollow hole 21 to fill the bone head part B with the bone cement from the leading end of the joining bolt 12 and the through-holes 23 formed to the peripheral surface on the leading end side of the joining bolt to solidify the bone cement.