To suppress deterioration of vacuum degree after sealing by closing a sluice valve arranged between vacuum space and an evacuation means and sealing after evacuation work of an apparatus having sealing vacuum space is completed, measuring the vacuum degree in the vacuum space after sealing, and judging the terminal of evacuation operation.

In this case where the vacuum space of a vacuum heat resistance piping 6 is evacuated, a suction port valve 5, a seal off valve 7, a vacuum valve 8, and a sluice valve 22 are opened, and preliminary sucking is started by a preceding step pump 3. Current-carrying to a baking heater 24 is started, a vacuum heat resistance piping 6 is heated, and degassing is promoted. When it reaches to a prescribed vacuum degree, a main exhaust pump 2 is started. When a sufficient vacuum degree is judged, the backing heater 24 is turned off, and the valve 32 is closed when the vacuum degree comes to a constant level. In this condition, it is left for a prescribed period, rising of pressure within its period is measured. When it is within a specified value, acceptance is judged, and sealing is carried out by operating the vacuum valve 8 so as to separate the vacuum valve 8 from an exhaust device.