PURPOSE: To maintain the recovery speed at the prescribed speed or above at which a prescribed rate of recovery is obtd. in a prescribed time by providing controllers which emit valve close signals when the recovery amts. in recovery tanks attain set values to the control valves of the recovery tanks respectively.

CONSTITUTION: Weight detectors 5a, 5b, 5c which measure the weights of recovery tanks 3a, 3b, 3c (which measure substantially the weights of the sublimable materials in the tanks) are justaposed to the respective tanks. Controllers 6a, 6b, 6c which are inputted with the results detected with said detectors, compare the same with the set values of the recovery amts. set with each phase of said tanks and emit the close signals for closing automatically the automatic control valves 2a, 2b, 2c of the recovery tanks when the tanks attain said set values are further provided respectively to the detectors 5a, 5b, 5c. Therefore, the prscribed overall recovery amt. is obtd. in the prescribed time and the efficiency of recovery is remarkably improved.