this case the leakage is at the sor side there is a high possibility that leakage abnormality occurs at every port therefore the above described operation assures higher certainty and reliability than detecting leakage at each port independently of the others and operating the associated cutoff valve if the leakage occurs at the exposure apparatus side such a port at which the leakage has occurred is isolated by the emergency cutoff valve 17 simultaneously therewith such information is transmitted through the communication cable 5 to each port control 26 to close the emergency cutoff valves 21a 21e of the respective exposure apparatuses this ensures with certainty the protection of the beryllium window 21 and the exposure apparatus 15 even in the worst case wherein the leakage is not intercepted by the emergency cutoff valve 17 fig4 shows another embodiment wherein a signal from a seismometer is used as a signal representing the abnormality of the sor exposure system in fig4 denoted at 30 is a seismometer which is placed on the same ground on which the sor exposure system is provided denoted at 31 is a signal processing means which is operable to compare the signal from the seismometer 30 with a certain set value and also to provide in a certain situation or situations an alarm in the form of an abnormality signal the signal processing means includes a.