A collector mirror exchanging apparatus is capable of safely and easily exchanging a collector mirror for collecting extreme ultra violet light emitted from plasma generated within a chamber of an extreme ultra violet light source apparatus. The collector mirror exchanging apparatus includes: a supporting base for supporting a collector mirror or a collector mirror structure; and a guiding rail disposed on the supporting base and regulating a moving direction of the collector mirror or the collector mirror structure; wherein at least the collector mirror is taken out of the chamber by moving the collector mirror or the collector mirror structure along the guiding rail on the supporting base.