There is provided a method for manufacturing a double-chamber container including an agent storage chamber and a solution storage chamber separated from each other by a weak seal portion, the method including the steps of: preparing a first sheet-like member including a first agent storage chamber forming portion and a first solution storage chamber forming portion whose one sides are joined to each other, as well as a second sheet-like member including a second agent storage chamber forming portion and a second solution storage chamber forming portion whose one sides are joined to each other; and forming the agent storage chamber and the solution storage chamber by joining the first and the second sheet-like members. The weak seal portion is formed by joining the one side of the first medical solution storage chamber forming portion and the one side of the second medical solution storage chamber forming portion.