It’s a futon drier. You can set a futon-sized big square plastic bag filled with hot air between the shiki-buton (mattress) and the kake-buton (comforter), and continue to allow hot air to circulate in the bag for about one hour to make futons dry. Futons become fluffy and soft after using the drier. Japan’s climate is humid, so futons tend to get moldy unless you dry them in the sunshine or use the futon drier. The futon drier can be used not only to dry futons but also to eliminate mites or heat futons.