A neutron beam irradiation system that irradiates an irradiated body with a neutron beam includes: a neutron beam generating section that is irradiated with a charged particle beam, thereby generating a neutron beam； an accommodation section that includes at least a moderator and accommodates the neutron beam generating section； a neutron beam converging section that converges the neutron beam which is irradiated to the irradiated body； a placement table on which the irradiated body is placed； and relative movement means that relatively moves the placement table so as to approach and be separated from the neutron beam generating section, the accommodation section, and the neutron beam converging section.
