AbstractTritium exposure gives rise to a considerable increase in the noise of a mass spectrometer. To avoid this impairment and apply the mass spectrometer to DT burning fusion devices, we developed a tritium compatible quadrupole mass spectrometer with tritium decontamination devices.It was observed that the noise level and width increased with tritium exposure: namely, the noise level increased to 100 times of the initial one owing to cumulative tritium exposure of 0.1 Torr s. The increase in the noise width, on the other hand, was about 30 times. It was confirmed that the increase in the noises is due to the tritium adsorbed on the surfaces of the inner walls of the vacuum system, quadrupole, and detector itself: the tritium in the gas phase played only a minor role. The noise level and width could not be effectively reduced by simple evacuation at room temperature. On the other hand, it was revealed that photon irradiation by halogen lamp caused both the noise level and width to reduce. Photon irradiation by mercury lamp acted similarly. The decontamination (i.e. removal of the adsorbed tritium) is not due to a thermal effect but to photon-induced desorption. These results indicate that the tritium contamination of the mass spectrometer can be removed in-situ by photon irradiation, although an improvement of the pumping system and photon irradiation device should be required.