PURPOSE: To ensure the profitability and the soundness of a radioactive substance storage facility including a storage for radioactive substance packs, without deteriorating the detection sensitivity for a degree of vacuum in the case of storing several storage containers.

CONSTITUTION: A vacuum control device incorporates depressurizing pipe lines 23 which are connected in parallel in each of groups into which several storage containers 21 are divided into, pressure sensors 24 for detecting depressurized conditions, a vacuum degree determining part 25 for selecting vacuum degree data and a vacuum control part 26 for operating a, vacuum generating means 22 in accordance with the selected vacuum degree data. Among the groups, the one having a worst vacuum degree is determined so as to operate the vacuum generating means 22, thereby the vacuum degree in the radioactive substance storage facility is maintained.