A neutron reflector bolt fastening structure is disclosed in which even upon relaxation in the fastening forces thereof being generated in tie rods for divided stage portions as a result of neutron irradiation, it is possible to press the neutron reflector firmly against a core vessel. The neutron reflector bolt fastening structure includes: a neutron reflector which includes of a plurality of divided stage portions and situated in a core vessel in a reactor vessel; a plurality of tie rods for fixing the neutron reflector to the core vessel; and a plurality of bolts for exclusively fixing the lowermost stage portion of the plurality of stage portions of the neutron reflector to the core vessel.