Abstract: A finger joint prosthesis for MP joint or PIP joint in which a socket has an opening at a portion thereof and a spherical face on an inner side thereof and is integrally formed with a stem on a side opposed to the opening, a head has a spherical portion fit to the spherical face via the opening and is integrally formed with a stem extending outwardly from the opening and a sheath for surrounding the stem of either of the socket and head is provided and the stem is movable slidably in an axial direction by adhering and fixing the sheath to a narrow cavity at a nearly disposed portion or a remotely disposed portion whereby the joint prosthesis is matched with motional characteristic of finger.