A process-liquid supply part includes: a supply tank configured to contain a process liquid; a level gauge pipe connected to the supply tank, the level gauge pipe being provided with level sensors for detecting a remaining amount of the process liquid contained in the supply tank; and a measuring part configured to measure a remaining amount of the process liquid based on signals from the level sensors provided on the level gauge pipe. Connected to the supply tank are a process-liquid supply pipe configured to drain the process liquid contained in the supply tank, and a process-liquid return pipe configured to introduce the process liquid drained through the process-liquid supply pipe to the supply tank. A connection pipe, in which an openable and closable valve is provided, disposed between the process-liquid supply pipe or the process-liquid return pipe and the level gauge pipe.