A constant-pitch microprism-array optical device has been developed. It is a modified version of the previously reported quasi-Fresnel lens [Kagoshima et al., Appl. Phys. Lett. 101, 163102 (2012)]. The modification eases the fabrication of the lens, although it degrades some of the focusing performance. It consists of twenty 50-mu m-wide right-angle microprisms, whose slope angles gradually increase to 67.8 degrees at the outer side. By inclining the array, the aspect ratio of the microprisms becomes large enough for X-ray use. The effective slope angle can be enlarged to 86.4 degrees at an inclination angle of 80.5 degrees. A 10-keV synchrotron beam with a size of 680 mu m (V) x 660 mu m (H) was two-dimensionally condensed to 130 mu m (V) x 380 mu m (H) with a photon flux density gain of similar to 3. We also show that the microprism array is suitable for practical use below the critical radiation dose rate. (C) 2013 AIP Publishing LLC.