A5052 aluminum alloy sheets were formed into concavo-convex shape by friction stir incremental forming. By the conventional friction stir incremental forming, sheet metals were formed from one side and formed into only concave or convex shape without supporting die. But in this study, an equipment for forming from both sides simultaneously was developed and it was tried to form the sheet metals into concavo-convex shape. First, strain distribution by single side forming was measured. To evaluate the forming accuracy by simultaneous forming, formed shapes by double side forming and single side forming with reversing the sheet for forming from both sides were compared. A5052 aluminum alloy sheets with the size of 100 mm x 100 mm x 0.5 mm were used for specimen. From the experimental results, it was conformed that since both sides simultaneous forming is possible to make the two products in one processing, it is possible to shorten the forming time to be half. Curved portion is easy to break. Because Strain of curve portion is bigger than straight portion. Forming accuracy of the center part of the sheet can be improved when the forming of the sheet to close the working distance.