The exposure device includes a polarizing plate and an illumination diaphragm. The polarizing plate is located in an optical path between a light source and a photomask, serving as a polarizing unit that polarizes an illuminating light from the light source in the first and the second direction orthogonal to the optical axis. The illumination diaphragm is a so-called quadruple illumination diaphragm, which includes four openings. The first opening and the second opening are located on a straight line running parallel to a third direction perpendicular to the optical axis and passing the center point of the illumination diaphragm, across the center point from each other. Likewise, the third opening and the fourth opening are located on a straight line running parallel to a fourth direction perpendicular to the optical axis and passing the center point, across the center point from each other.