A thin film deposition apparatus and a method of maintaining the same are disclosed. In one embodiment, a thin film deposition apparatus includes: a chamber including a removable chamber cover; one or more reactors housed in the chamber; a chamber cover lifting device connected to the chamber cover. The chamber cover lifting device is configured to move the chamber cover vertically between a lower position and an upper position. The apparatus further includes a level sensing device configured to detect whether the chamber cover is level, and a level maintaining device configured to adjust the chamber cover if the chamber cover is not level. This configuration maintains the chamber cover to be level as a condition for further vertical movement of the chamber cover.