PURPOSE: To provide a function for dwindling the strength to an intramedullary needle by inserting removably a reinforcing member into a cylindrically formed pipe of the intramedullary needle and pulling out stepwise the reinforcing member in accordance with the assimilation condition of a fractured bone part.

CONSTITUTION: A cylindrical intramedullary needle main body 1 is prepd. by molding a flexible titanium alloy into a cylindrical shape and a ring-like stopper 5 for a reinforcing member projecting inside is provided in the bottom hole 4 of a needle bottom 2 and a semi-spherical lid is covered on the mouth hole 6 of a needle head 3 from the outside. The flexible reinforcing member 11 made of the titanium alloy inserted in the intramedullary needle main body 1 consists of a column-like stem 12 and cylindrical sheaths 13 and 14 and the head of the stem 12 is projected from the head of the sheath 13 and the head of the sheath 13 is projected from the head of the sheath 14 and the head of the sheath 14 is projected from the mouth hole 6 of the needle head 3. In addition, on the head part of each reinforcing member 11, a small hole is opened as a hook hanger 15 for pulling out. After waiting for starting of assimilation of the fractured bone end, the stem 12 is at first pulled out and then, while the adhesion condition is observed, the sheath 13 is pulled out and finally, the sheath 14 is pulled out to decrease stepwise the strength.