An ink receptacle for an on-demand type ink jet printer in which an ink reservoir for storing ink which is to be ejected from an ink jet head is mounted on a carriage. A relatively thick flat housing which is made of non-flexible resin and open at one surface and a single flexible film are bonded together, the film covering the open side of the housing. The housing and the film cooperate to define a relatively large first ink chamber having an opening which is open to the outside and a relatively small second ink chamber also having an opening which is open to the outside. That part of the film which covers the first chamber is deformable to vary the volume of the first chamber corresponding to an amount of ink remaining in the chamber.