Friction stir incremental forming is a new sheet forming process that combined incremental forming and friction stir welding together. It can manufacture the hard-to-work material product of complex shape under the traditional CNC machine and only use a hemispherical tool. In most reports using friction stir incremental forming process, sheets were formed into concave shape. On the other hand, sheets were formed into convex shape with simple back support dies by the conventional incremental forming. In this study, sheet metals were formed into convex shape by friction stir incremental forming process with a back support die. A5052-H34 aluminum alloy sheets were used for specimen. The dimension of the sheet was 100 mm x 100 mm x 0.5 mm. A hemispherical stick tool with a diameter of 6 mm was used for forming. The shape of back support die is a frustum of pyramid. The sheet was fixed to the upper face of the back support die by a bolt and formed along the die shape by pushing with the forming tool. Tool rotation rate and fool feed rate were changed and formability was evaluated by the minimum formable wall angle. From the experimental results, formability was maximum and the wall angle was 25 ° when the tool feed rate was 1000 mm/min and the tool rotation rate was 10000 rpm. The formed shapes with and without the back support die were compared. The formed shape with the back support die was closer to the objective shape, especially at the flange part.