A KB mirror requires two elliptical mirrors with vertical and horizontal working directions located in front of and behind the optical axis. Their magnification ratios are different. A Montel mirror consists of two identical elliptical mirrors adjacent to each other. By using the area near the junction as an optical surface, 2D focusing with the same vertical and horizontal magnification ratio is realized. A Montel mirror enables limiting the range of the widening of the downstream incident angle in comparison with a KB mirror. JTEC's Montel mirror has achieved 50 nm diameter focusing on the beamline of a major synchrotron radiation facility.