expansion part with binding of a fixing member 211 fig5 c and 5 d show that a sphere like double layer covering member 210 is fixed to a protrusion 130 of the expansion part with a fixing member 211 fig6 a and 6 b illustrate two embodiments of joining structure between the expansion part and an auxiliary expansion part of the device for bone fixation according to the present invention fig6 a shows the fixing end 120 of the expansion part is detachably to engage with the joining end 320 of the auxiliary expansion part with screw threads fig6 b shows the fixing end 120 of the expansion part is detachably to join with the joining end 320 of the auxiliary expansion part with locking fig7 a 7 b 7 c and 7 d illustrate two embodiments of joining structures between the expansion part and an operating shaft of the auxiliary expansion part of the device for bone fixation according to the present invention fig7 a shows a locking groove 131 disposed at the top of the expansion part and a locking protrusion piece 311 of the operating lever 310 form detachable engagement the operation lever 310 is detached and replaced with the injection tool after the expansion part is expanded by the operation lever 310 the stem 340 of the auxiliary expansion part also has a locking protrusion piece 321 to detachably lock with the retaining groove 121 of the expansion part as well fig7 b to 7 e show that with an.