Disclosed is a simple and compact optical element holding system in a projection optical system which enables correction of astigmatism without causing comatic aberration. The holding system includes a relative angle adjusting system for tilting one of at least two optical elements with respect to an optical axis, and a tilt angle adjusting system for tilting the at least two optical elements integrally, by the same amount as and in an opposite direction to the tilt direction of the relative angle adjusting system, with respect to the optical axis and separately from the relative angle adjusting system.