PURPOSE: To enhance the reliability against vacuum leakage, to reduce the number of radiated parts and to prevent the damage of a carbon membrane due to the erroneous operation of a valve by reducing the number of parts to the connection pipe of a nuclear fusion device and a neutron particle analyser.

CONSTITUTION: A drive member 21 provided with a carbon membrane 10 is moved along upper and lower guide members 22, 23 and the communication hole 24 of the drive member 21 and the through-holes 24 of the respective guide members 22, 23 are aligned to allow a nuclear fusion device and a neutron particle analyser to communicate with each other and the drive member 21 is moved along the guide members 22, 23 to positionally shift the communication hole 24 from the through-holes 30, 32 to cut off the nuclear fusion device and the neutron particle analyser.