PROBLEM TO BE SOLVED: To provide a surgical instrument for osteosynthesis capable of contributing to cost reduction of the surgical instrument including a bone plate, and capable of facilitating the work for reduction.SOLUTION: The surgical instrument 100 for osteosynthesis is for reducing and securing a fractured bone piece 401 to a bone body 400. The surgical instrument 100 includes: an implant 110 having at least one through slot 111 to be disposed in the bone body and at least one screw hole 113 to be fixed to the bone piece a fixing member 120 having a rack 121 to be detachably fixed to the implant 110 and a rotating member 130 having a gear part 131 to be engaged with the rack 121 and a rotating shaft 132 extending coaxially with the axis of the gear part 131, inserted into the through slot 111 to be inserted into the bone body 400. The direction of arrangement of a plurality of rack teeth composing the rack 121 of the fixing member 120 is parallel to the longitudinal direction of the through slot 111 of the implant 110.
