To firmly and precisely position a limb by utilizing the intrinsic form of a bone inherent in the limb when it is necessary to securely, precisely and accurately position and fix a region of a living body for the measurement, diagnosis, treatment, surgery, etc.

The living body fixing device 96 is a device for fixing a lower limb (especially the proximal part) as the limb. A peroneal bone head fixing part 120 with a positioning pad 56 and an inner side fixing mechanism 94 with an inner side pad 96 are disposed on both sides of the lower limb respectively. The lower limb can be held between the positioning pad 56 and the inner side pad 96 by advancing the inner pad 96 while the positioning pad 56 is positioned and made to abut to the peroneal bone head of the lower limb via a thin dermal layer. Since such a characteristic bone region as the peroneal bone which can be specified from outside via the thin dermal layer is a reference for positioning, the lower limb can be fixed with excellent reproducibility, and can be securely held.