The present invention relates to a method for reduce treating ballast water which has been subjected to a biocidal treatment with a chlorine-based oxidizing agent or an oxygen-based oxidizing agent, by using a tablet or pellet of sodium sulfite. The laundry in the laundry treating chamber may be imaged and a state of dryness of the laundry determined based on the imaging of the laundry. In the structure, an elastic seal member is compressed within the screw hole, in an axial direction of the screw member, and is therefore deformed radially outwards by compression force that is created by tightening of the screw member, and an air-tight state of the screw hole is maintained by deformation of the elastic seal member. A maximum selector selects a maximum object length from among the plurality of candidate object lengths.