A projection optical system PL for forming an image of a first plane M on a second plane P has at least one first wedge prism 4 each of an entrance surface and an exit surface of which has a plane and in which a predetermined first wedge angle is made between the plane of the entrance surface and the plane of the exit surface, and when a coordinate system is so defined that a Z-axis direction is set along a direction of a normal to the first plane M, an X-axis direction along a direction of an intersecting line between the plane of the entrance surface and the plane of the exit surface, and a Y-axis direction along a direction perpendicular to the Z-axis direction and the X-axis direction, the first wedge prism 4 is arranged rotatably substantially around the Y-axis direction.