To provide a sheet material superposition method for positioning thin and flexible sheet materials and superposing one over the other over the entire surface of the sheet material with high accuracy.

This sheet material superposition method at least includes: a first process of first holding a first sheet material on a first sheet material holder under reduced pressure and holding a second sheet material on a second sheet material holder under reduced pressure; a second process of reversing the second sheet material holder and superposing the same on the first sheet material holder under reduced pressure; and a third process of detaching the second sheet material from the second sheet material holder and removing the second sheet material holder with the second sheet material left on the first sheet material. After the third process, the second and third processes are repeated to stack a plurality of sheet materials.