In a scanning-type projection exposure system, curvature of a movable mirror that is used to measure mask stage coordinate positions is determined while the mask stage is moved in the scanning direction, by measuring coordinate positions, perpendicular to the scan direction, of the mask stage and of a mask mark elongated in the scan direction. The results of the measurements are used for correcting or compensating positional deviation during scanning. Rotational deviation of a mask pattern area is determined and is corrected or compensated. Also, a mask is aligned with respect to a coordinate system of the mask stage as pre-processing for exposure, using a mask alignment mark having two crossing linear patterns and determining a coordinate position of the crossing point by moving the mask relative to an observation area.