Dust that is accumulated in an exhaust passage provided in a chamber, the exhaust passage for discharging gas in the chamber of a semiconductor crystal manufacturing device, is removed by being sucked from the outside of the chamber. Moreover, an opening and closing valve for cleaning that is detachably attached to an opening of the exhaust passage, the opening facing the chamber, is opened and closed intermittently in a suction state. Furthermore, the opening and closing valve for cleaning is driven by a valve driving unit. The dust accumulated in the exhaust passage is removed efficiently, whereby the time required to clean the exhaust passage is shortened and fluctuations of the pressure inside the chamber when a semiconductor crystal is manufactured are suppressed.