A fluoride sintered body suitable for a moderator which moderates high-energy neutrons so as to generate neutrons for medical care with which an affected part of the deep part of the body is irradiated to make a tumor extinct comprises MgF2 of a compact polycrystalline structure having a bulk density of 2.90 g/cm3 or more and as regards mechanical strengths, a bending strength of 10 MPa or more and a Vickers hardness of 71 or more.