Clogging of a distillation column by polymerization caused by a change of the production rate of acrylic acid, is prevented to carry out a stabilized operation over a long period. The source and the drain of each FET capacitor are coupled to one another. A communications-terminal selecting unit is configured to select out of the communications terminals one which has the need to change the downlink transmission rate in accordance with the downlink transmission qualities obtained at the transmission-quality obtaining unit. The tensioning system has a first idler plate configured to bias a first idler pulley against the drive belt when the drive is rotating the shaft in the first direction and a second idler plate configured to bias a second idler plate against the drive belt when the drive is rotating the shaft in a second direction.