The image data forming portion system of the present invention forms the image data of the image comprising ulna and radius, and image data identification part 16 identify the image part of correspondence what bone and the image part of the soft portion's tissue of corresponding what in image data. Image data of the defiber configuration part 20 according to identification Hou, setting is clipped in the defiber of the image part point of soft portion's tissue between the bone in ulna and radius by corresponding what, skeletal image separation unit 22 is according to defiber, and the image part by that will correspond to what bone is separated into 2, and extract the image part comprising ulna out. Belemnoid particular portion 24 carrys out specific processus styloideus ulnae according to the shape of the image part comprising ulna.本發明之影像資料形成部係形成包含尺骨與橈骨之影像的影像資料，影像資料識別部16在影像資料內識別對應於骨骼之影像部分與對應於軟部組織之影像部分。分離線設定部20依據識別後之影像資料，設定通過對應於夾在尺骨與橈骨中之骨間軟部組織的影像部分之分離線，骨骼影像分離部22依據分離線，並藉由將對應於骨骼之影像部分分離成2個，而抽出包含尺骨之影像部分。莖突特定部24依據包含尺骨之影像部分的形狀來特定尺骨莖突。
