A triangular variable shaped electron beam lithography method using the cell projection method is proposed. The shaped beams are formed by a conventional rectangular beam method and variable triangular apertures. This method has three significant characteristics : The plural kind of triangles can be made. This increases the pattern flexibility and decreases the number of shots. The position of one corner of the triangles is automatically determined. Therefore, there is no fluctuation of the triangular beam position and the size of the triangle can be varied with high precision. The triangular apertures are located such as to minimize the deflection distance. This realizes high speed and high precision beam formation. With these characteristics, this method is expected to be used for high speed and high precision mask fabrication.