A duplex container comprises a container main body provided with a cutting unit for cutting a partition wall formed in a sub-container so that when the sub-container is mounted on the container main body, the partition wall is cut and the content contained in the sub-container flows into the container main body, wherein even if the sub-container is mounted on the container main body and the partition wall the sub-container is cut while the pressure in the sub-container is high, the sub-container can be depressurized at the time of cutting the partition wall. The container (3) is opened by inserting a cutting unit (221) into the cylindrical hanging portion (312), and by cutting the partition wall (30a) under the state that the outer peripheral surface of the cutting unit (221) is brought in close contact with the inner peripheral surface of the cylindrical hanging portion (312), wherein the container (3) is provided with a partition wall (30a) defining a part of a storage chamber (30), and a cylindrical hanging portion (312) including a portion at which the partition wall (30a) is formed. The cutting unit (221) has a shape in which an upper side of a cylindrical portion standing parallel with the axial direction is cut to be inclined relative to the axial direction, and a notch (221c) is formed on the upper end surface of the cutting unit (221).