An ink tank in which an air communication passage and a pressure regulator valve passage are formed by covering grooves, etc., with a film is fabricated in a simple manufacturing process. Specifically, an atmosphere communication hole and a major part of an air communication passage are formed in the same surface on which a film for forming a valve passage is attached. By virtue of this, the process of attaching a major part of the air communication passage film and the process of attaching the valve film can be performed in a single process step. This simplifies the process of attaching the films.