explained referring to figures fig7 shows a coupling process in this figure 25 denotes a lock mechanism to firmly fix so that the two spaces 10 and 15 do not separate more than a defined distance and instruments to construct the lock mechanism in the respective space are arranged the 28 denotes a doughnut type hollow rubber ring which acts as a seal in coupling the two spaces 10 and 15 in this construction when the two spaces 10 and 15 are coupled the lock mechanism firmly fixes the spaces 10 and 15 the hollow rubber ring 28 expands by air running into this ring 28 an exterior wall forming each space is pressed by the rubber ring 28 for closing up between the two space invasion of external air into the spaces 10 and 15 is prevented and the two spaces 10 and 15 become an airtight condition when the coupled two spaces 10 and 15 are separated the air run into the hollow rubber ring 28 is exhaled in such a degree as the lock mechanism 25 is unfastened and the lock mechanism 25 is discharged doing this coupling and separating of the two spaces 10 and 15 can be optionally and easily carried out hereinafter an operation such as maintenance in a clean space system having a structure.