A multi-chamber container having an outlet port, which is usually closed and is opened in cooperation with an expanded deformation of the bag upon the opening of the medical bag and aiming to obtain more reliable opening of the medical bag upon the separation of the partition wall. The outlet port firmly welded to a strong seal 14-1 at an outer periphery has a base portion 12-1, from which a rectangular cross-sectional shaped portion 12-6 integrally extends. The rectangular cross-sectional shaped portion 12-6 has, at its top surface, a U-shaped groove, the bottom surface 30 of which functions as a weak portion 30. To a portion 33 inward from the U-shaped groove 39 at the top wall of the rectangular cross-sectional shaped portion 12-6, the opposed surface of the medical bag is firmly welded by a point seal 34. An expansion of the medical bag upon its opening generates an outside force, resulting in a breakage at the weak portion 30, so that a rotating movement of the portion 33 under a pull-tab manner is generated. As a result, an opening 36 for a communication of the inside of the medical bag to the inside of the outlet port is formed at the location of the outlet port occupied by the portion 33 prior to the formation of the opening 36.
