A maintenance device has a cover and a fixing member. The cover is in a vacuum atmosphere during substrate processing, is formed to have a size corresponding to a boundary line between a first part and a second part of a processing container, which can be separated into the first part and the second part, or an opening surface separating the first part and the second part, and has airtightness, and visual transparency at least in a part. The fixing member fixes in an airtight manner the cover along the boundary line between the first part and the second part of the processing container or to the opening surface separating the first part and the second part.