A method for manufacturing a double-chamber container including a medical agent storage chamber and a medical solution storage chamber separated from each other by a weak seal portion, the method comprising the steps of: forming a first sheet-like member by joining one side of a first medical agent storage chamber forming portion and one side of a first medical solution storage chamber forming portion in the form of a strip, forming a second sheet-like member by joining one side of a second medical agent storage chamber forming portion and one side of a second medical solution storage chamber forming portion in the form of a strip, forming said medical agent storage chamber and said medical solution storage chamber by arranging said first sheet-like member and said second sheet-like member to face each other and then joining said first sheet-like member and said second sheet-like member, wherein said medical agent storage chamber is formed by joining the other sides (11B to 11D) of said first medical agent storage chamber forming portion and the other sides (21B to 21D) of said second medical agent storage chamber forming portion, said medical solution storage chamber is formed by joining the other sides (12B to 12D) of said first medical solution storage chamber forming portion and the other sides (22B to 22D) of said second medical solution storage chamber forming portion, said weak seal portion is formed by joining said one side of said first medical solution storage chamber forming portion and said one side of said second medical solution storage chamber forming portion, and said first sheet-like member and said second sheet-like member are peeled off from each other in said weak seal portion, and thereby, said medical agent storage chamber and said medical solution storage chamber communicate with each other. forming a first sheet-like member by joining one side of a first medical agent storage chamber forming portion and one side of a first medical solution storage chamber forming portion in the form of a strip, forming a second sheet-like member by joining one side of a second medical agent storage chamber forming portion and one side of a second medical solution storage chamber forming portion in the form of a strip, forming said medical agent storage chamber and said medical solution storage chamber by arranging said first sheet-like member and said second sheet-like member to face each other and then joining said first sheet-like member and said second sheet-like member, wherein said medical agent storage chamber is formed by joining the other sides (11B to 11D) of said first medical agent storage chamber forming portion and the other sides (21B to 21D) of said second medical agent storage chamber forming portion, said medical solution storage chamber is formed by joining the other sides (12B to 12D) of said first medical solution storage chamber forming portion and the other sides (22B to 22D) of said second medical solution storage chamber forming portion, said weak seal portion is formed by joining said one side of said first medical solution storage chamber forming portion and said one side of said second medical solution storage chamber forming portion, and said first sheet-like member and said second sheet-like member are peeled off from each other in said weak seal portion, and thereby, said medical agent storage chamber and said medical solution storage chamber communicate with each other.