A dry room for gas substitution has a drying chamber to receive dry air from a dry air supply device. Gas is circulated between inside the drying chamber and the dry air supply device. An airtight container is accommodated in the drying chamber. A low dew point gas supply device coupled to the airtight container removes moisture and supplies low dew point gas to the airtight container via a filter that removes foreign matter. An inert gas purification device removes oxygen and supplies an inert gas to the airtight container. A gas exhaust passage exhausts gas in the airtight container to outside of the drying chamber. The low dew point gas supply device and the inert gas purification device are independently provided so that moisture removal via the low dew point gas supply device is adjusted independently of oxygen removal via the inert gas purification device.