A neutron capture therapy apparatus (1A, 1B) comprising: an accelerator which is configured to emit a charged particle beam; a target which is configured to be irradiated with the charged particle beam to generate a neutron beam; a beam transport path that is configured to transport the charged particle beam, which is emitted from the accelerator, to the target, wherein the target is disposed in a downstream end of the beam transport path of the charged particle beam; a current detection portion which is configured to detect a current value of the charged particle beam, wherein the current detection portion is provided inside the beam transport path along an inner wall of the beam transport path in a state of being insulated from the inner wall, wherein the current detection portion is insulated from the downstream end of the beam transport path in which the target is disposed, and wherein the current detection portion is adapted to measure a current of the charged particle beam which comes into contact with the current detection portion; and a control portion that is configured to stop the irradiation of the target with the charged particle beam by assuming that the position at which the target is irradiated with the charged particle beam is abnormal when the current value detected by the current detection portion becomes less than or equal to a lower limit value which is smaller than a reference current value, or greater than or equal to an upper limit value which is greater than the reference current value, by setting a current value detected by the current detection portion when the position at which the target is irradiated with the charged particle beam is normal, as the reference current value. an accelerator which is configured to emit a charged particle beam; a target which is configured to be irradiated with the charged particle beam to generate a neutron beam; a beam transport path that is configured to transport the charged particle beam, which is emitted from the accelerator, to the target, wherein the target is disposed in a downstream end of the beam transport path of the charged particle beam; a current detection portion which is configured to detect a current value of the charged particle beam, wherein the current detection portion is provided inside the beam transport path along an inner wall of the beam transport path in a state of being insulated from the inner wall, wherein the current detection portion is insulated from the downstream end of the beam transport path in which the target is disposed, and wherein the current detection portion is adapted to measure a current of the charged particle beam which comes into contact with the current detection portion; and a control portion that is configured to stop the irradiation of the target with the charged particle beam by assuming that the position at which the target is irradiated with the charged particle beam is abnormal when the current value detected by the current detection portion becomes less than or equal to a lower limit value which is smaller than a reference current value, or greater than or equal to an upper limit value which is greater than the reference current value, by setting a current value detected by the current detection portion when the position at which the target is irradiated with the charged particle beam is normal, as the reference current value.