PURPOSE: To exhaust automatically residual air to the outside of the system by storing a double layer membrane prepd. by holding air-communicating gaps in the longitudinal direction of hollow fiber membrane between hydrophobic microporous flat membranes and a bundle of hollow fiber membranes consisting of a number of hollow fiber membranes under their wound condition in a case.

CONSTITUTION: This hollow fiber membrane module is prepd. by a process wherein a hollow fiber membrane bundle 2 prepd. by tying a flat bundle of hollow fiber membranes and a double layer membrane 3 in a bundle is wound and inserted into a case 1 and after the one end (a potting part) is fixed with an adhesive 4, the potting part is cut. The inner side of the case is opened thereby on the end face to open the cut face side of the potting part. In addition, at the cut face of the potting part, the hollow fiber membrane as well as the double layer membrane 3 are opened. In addition, this double layer membrane 3 is formed by laminating hydrophobic microporous plane membranes together and bonding them by means of heat fusion, etc., in such a way that the heat- sealed parts with a fixed width exist at a fixed interval parallel in the longitudinal direction of the hollow fiber membrane.