The present invention provides a backing metal fixture which is excellent in constructability and stability with fixing an external wall, and an external wall constructing structure using the backing metal fixture. A backing metal fixture used for fixing an external wall to a skeleton via a securing metal fitting and a heat insulating material placed on a front surface of the skeleton, comprising: a butting flat plate portion to be butted against a rear surface of the securing metal fitting having an opening in the center area to allow a fixing member to go through, and a first leg unit and a second leg unit erected rearward from the butting flat plate portion, wherein the second leg unit is erected from a position closer to the opening than the first leg unit.