A method for reinforcing a weak sealed portion of a multi-chamber medical container, comprising: a multi-chamber container forming step for forming a multi-chamber medical container, comprising; a first container portion for containing a medicine, a second container portion for containing a medical solution, disposed adjacent to the first container portion, an empty container portion disposed adjacent to an opposite side of the second container portion with respect to the first container portion, a pair of lateral side strong sealed portions which are disposed while spaced from each other in a width direction crossing a medical solution discharge direction from the second container portion toward the empty container portion through the first container portion, and form both side end portions of each of the container portions, a medical solution side weak sealed portion which is provided across each of the lateral side strong sealed portions and forms a partition between the first container portion and the second container portion, and is opened when a pressure inside the second container portion becomes high, and a discharge side weak sealed portion which is provided across each of the lateral side strong sealed portions and forms a partition between the first container portion and the empty container portion, and is opened when a pressure inside the first container portion becomes high, wherein each container portion has a front surface side film and a back surface side film which are sealed by each of the sealed portions and overlapped with each other; and characterized by a reinforcement film bonding step for bonding the reinforcement film for reinforcing the discharge side weak sealed portion on the surfaces of the medical solution side weak sealed portion, the discharge side weak sealed portion, and the pair of lateral side strong sealed portions so as to cover the surface of at least either one of the front surface side film and the back surface side film of the first container portion, wherein the reinforcement film bonding step includes a step of bonding the reinforcement film on the surfaces of the medical solution side weak sealed portion, the discharge side weak sealed portion and the pair of lateral side strong sealed portions so as to be spaced from a first border of the discharge side weak sealed portion with the first container portion to the downstream side of the discharge direction and so as not to bond to the first container portion. a multi-chamber container forming step for forming a multi-chamber medical container, comprising; a first container portion for containing a medicine, a second container portion for containing a medical solution, disposed adjacent to the first container portion, an empty container portion disposed adjacent to an opposite side of the second container portion with respect to the first container portion, a pair of lateral side strong sealed portions which are disposed while spaced from each other in a width direction crossing a medical solution discharge direction from the second container portion toward the empty container portion through the first container portion, and form both side end portions of each of the container portions, a medical solution side weak sealed portion which is provided across each of the lateral side strong sealed portions and forms a partition between the first container portion and the second container portion, and is opened when a pressure inside the second container portion becomes high, and a discharge side weak sealed portion which is provided across each of the lateral side strong sealed portions and forms a partition between the first container portion and the empty container portion, and is opened when a pressure inside the first container portion becomes high, a reinforcement film bonding step for bonding the reinforcement film for reinforcing the discharge side weak sealed portion on the surfaces of the medical solution side weak sealed portion, the discharge side weak sealed portion, and the pair of lateral side strong sealed portions so as to cover the surface of at least either one of the front surface side film and the back surface side film of the first container portion, wherein the reinforcement film bonding step includes a step of bonding the reinforcement film on the surfaces of the medical solution side weak sealed portion, the discharge side weak sealed portion and the pair of lateral side strong sealed portions so as to be spaced from a first border of the discharge side weak sealed portion with the first container portion to the downstream side of the discharge direction and so as not to bond to the first container portion.