A multi-chamber container of two liquid mixing type, aiming for obtaining an increased reliability for preventing an administration from being practiced under a non separated condition of a weak seal.The medical bag 10 has an outer peripheral strong seal 14 and a weak seal 18 for separating the space inside the medical bag into two partitions 20 and 22. At the tip end of an outlet port 12, a flap 28 as a valve member is provided, which usually closes the outlet port 12 to the space inside the medical bag. The flap 28 is connected to the opposite surface of the medical bag, so that the flap 28 is displaced in cooperation with an expansion deformation of the medical bag as obtained when the weak seal 18 is opened, resulting in opening of the outlet port 12. The flap is formed with a small hole 44 for limiting a liquid flow amount to a small value. When an infusion operation being started under the non-opened state of the weak seal, the liquid flow amount to the outlet port is restricted to a small amount by the small hole 44, thereby notifying the non-opened state of the weak seal and warning that the weak seal should be opened.