Abstract: In a method of automatic positional alignment of substrate and screen mask in electrical paste screen printing, the coordinates (X1, Y1), (X2, Y2) of points A, B on a substrate 10 are obtained with a first camera, while the coordinates (X3, Y3), (X4, Y4) of points A', B' on a screen mask 33 are obtained with a second camera. Then, the coordinates of the middle point P1 between the points A and B, and the coordinates of the middle point P2 between the points A' and B' are obtained, based on the results of which positional discrepancies .DELTA.X, .DELTA.Y between the substrate 10 and the screen mask 33 in the directions of X and Y are obtained. Subsequently, the substrate 10 is rotated horizontally with the middle points P1 and P2 superposed until a line segment L1 connecting the points A and B coincides with a line segment L2 connecting the points A' and B', as a result of which a positional discrepancy .theta. in the direction of horizontal rotation is obtained. If the positional discrepancies .DELTA.X, .