To safely and accurately cut and remove a bone around facies articularis tibiae.

In this osteotome 9, an upper end part is connected to an oscillator S, a driving shaft 9a is arranged in an intermediate part, a lower face touching the facies articularis tibiae in osteotomy is arranged in a cutting blade part 9b arranged in the lower end part and shaped into a rectangle in a plane view, and a cutting blade ridge is formed in the ridge line part in which the lower face and the side face cross each other. In the center of the cutting blade part 9a, a fitting hole receiving the point part of a rod 1 protruded from the tibia medullary cavity is formed.