Abstract: A gas leakage detection apparatus is described comprising a mass spectrometer with which there is associated a first pumping device for creating a relative vacuum in the apparatus, a selective pumping device having a first pumping speed for air and a second pumping speed for the gas which is to be analyzed, said second pumping speed being lower than the said first pumping speed, and a throttling device connected between the selective pumping device and the first pumping device, this throttling device having an opening chosen so as to let through a flow which is very small compared with the flow produced by the selective pumping device for the air.