A metal plate for producing a flat tube including a metal body having a joint portion, first and second flat wall forming portions connected by the joint portion, reinforcing wall forming portions projecting from the first and second flat wall forming portions and extending in a longitudinal direction of the first and second flat wall forming portions, and side wall forming portions projecting from opposite side edges of the metal body, respectively. The joint portion has a ridge which makes the joint portion thicker than the first and second flat wall forming portions. The ridge, the reinforcing wall forming portions and the side wall forming portions are projecting in a same direction. The metal body bends into a hairpin shape at boundaries formed between the ridge of the joint portion and the first and second flat wall forming portions.