There is provided a method for manufacturing a joined body using a rotary tool with a stirring pin to perform friction stirring on a composite body having a first surface and a second surface that is different from the first surface. In the composite body, metal members are combined together in a joined arrangement. The method includes the steps of: forming the composite body by combining the metal members in the arrangement; fixing the composite body in a state where the metal members are combined together; performing friction stir welding by inserting the stirring pin through the first surface into the composite body that has been fixed; rotating the fixed composite body such that the second surface is in a positional relationship to face the rotary tool; and performing friction stir welding by inserting the stirring pin through the second surface into the fixed composite body.