A flat-field fastf-ratio reflecting focal reducer which consists of two mirrors is described (figure 1). It can be used particularly for the Cassegrain focus withf-ratio 4–6, and thus anf-ratio 1–2 can be obtained. By way of removing the secondary mirror of the Cassegrain system and choosing the shapes of the two mirrors of focal reducer, not only can the third-order spherical aberration, coma, astigmatism and curvature of field be eliminated simultaneously, but the high-order aberration can also be reduced. This focal reducer has a field of view of 12-24 arc min and its focus is accessible. In this paper an example and its spot diagram are given. A modification of the focal reducer can also be used for prime focus.