There is provided a neutron capture therapy device which irradiates a patient with a neutron beam. The neutron capture therapy device includes a cyclotron configured to emit a charged particle beam a target, a scanning electromagnet, and the like configured to generate a neutron beam by being irradiated with a charged particle beam a current monitor configured to detect a current value of a charged particle beam with which the target is irradiated and a gamma ray detection unit and a radiation dose calculation section configured to detect a radiation dose of a gamma ray which is generated from the target in response to irradiation of the charged particle beam.
