To obtain a mixing device for mixing bone cement consisting of a liquid component in the package and powder component in the bag in a completely sealed state.

The mixing device includes a mixing member 1 having a mixing space 2 for mixing components 11, 12. There is provided with a vacuum unit 17 for generating vacuum within the mixing space 2 in a manner mixing components 11, 12 under vacuum conditions. Also, there is provided with a mixing means 10 so as to mix components 11, 12 in the mixing space 2. A sealing vessel 20 having a component 12 is fed into an outside vessel 22. The sealing vessel 20 can be opened as being fed into the outside vessel 22, and the component 12 is permitted to flow into the component 11 within the other mixing space 2, thereby mixing the components 11, 12. Herein, the outside vessel 22 and one end periphery 5 or 3 of the mixing member 1 can be interconnected, and the mixing means 10 is mounted movable to an opposite side end peripheral part 3 or 5 of the mixing member 1 with respect to the mixing space 2.