Abstract: A carrier 2 that holds a wafer 3 is shut off from the outside environment by causing a box 1 and a box plate 4 to come into intimate physical contact by means of a box plate joiner 7. When this is done, a switch 9 of a electricity charger/discharger 5 is set to a first position so as to charge electricity to the box 1 via power supply circuit 10, causing dust within the box 1 to be attached to the inner walls 1a of the box 1 by electrostatic attraction. Thereafter, even if the box plate 4 that was joined to the box 1 is removed from the electricity charger/discharger 5, because the electricity of the box 1 remains, the electrostatic attraction effect persists. Thus, once dust is attracted, it remains attached to the inner walls 1a of the box 1.