A reflective optical element includes a first, inner surface region for reflecting a first inner beam portion of a light beam impinging on the reflective optical element in order to form a first reflected light beam, and at least one second, outer surface region for reflecting at least one second outer beam portion of the impinging light beam for forming at least one second reflected light beam. The second surface region is designed to reduce a beam cross section of the second reflected light beam by comparison to the first reflected light beam such that the second reflected light beam extends along a superposition length completely within the first reflected light beam. In addition a beam guiding device has at least one such reflective optical element and an EUV-beam generating device has such a beam guiding device.