To improve mountability and kinetic properties by positioning the supporting surface of a head part having the joint surface, supporting surface and connecting part of a prosthesis device directly in juxtaposition with the humerus on a cut proximity end side and functioning this surface as a collar part.

The process device 10 to be mounted on the regulated humerus 12 is composed of a main body section 24 and a head section 14. The main body section 24 is supported in the humerus 12. The head section 14 is provided with the supporting surface 20 directly joined to the proximity end side bone surface 13 and is provided with a joint forming surface 18. When the main body section 24 is adequately arranged within the humerus 12, a proximal end surface part 26 exists lower than the proximity end side bone surface 13 and a tapered stem part 16 is accepted in a tapered hole part 33. The alignment characteristic between the tapered stem part 16 and the head part 14 is thereby held by the tapered sections 22 and 34. As a result, the mountability and kinetic properties may be improved.