Method for manufacturing container and method for separating inner layer

A method for manufacturing a container that includes a casing configured to contain a content, wherein the casing includes an inner layer having an inner layer opening for supplying the content to an outside and an outer layer covering the inner layer and having an air communication port to communicate between a space between the outer layer and the inner layer and the outside, the method comprising:

• preparing, as the casing, a casing in which at least part of the inner layer and at least part of the outer layer are in contact with each other;
• inserting a support column inside the inner layer through the inner layer opening of the prepared casing;
• and after inserting the support column,
• separating the inner layer from the outer layer by supplying air into the space through the air communication port to bring part of the separated inner layer into contact with the support column,
• wherein the support column includes a columnar portion and an extending portion extending from the columnar portion in a direction intersecting a longitudinal direction of the columnar portion.