A neutron capture therapy system includes a neutron beam irradiation unit that applies neutron beams, a treatment table on which an irradiation object irradiated with the neutron beams is mounted, a storage unit that stores distribution data indicating a distribution of hydrogen atoms or nitrogen atoms of a part to be irradiated of the irradiation object, a gamma ray detection unit that detects gamma rays generated from the irradiation object due to irradiation with the neutron beams, and a neutron flux distribution calculation unit that calculates a distribution of neutron flux in the irradiation object on the basis of the distribution data stored in the storage unit and gamma ray distribution data detected by the gamma ray detection unit.
