A flash X-ray diffraction (FXD) system with the Blumlein circuit and with an image intensifier has been developed for observation of crystal structures in an extremely short time such as that of the shock-compressed state of solids. The flash X-ray generator consists of a very low impedance (0.4 ohm as calculated) transmission line, whose dimensions are 20 cm in diameter and 600 cm in length, an X-ray radiation gap, and a pressurized-gas gap switch. The X-ray pulse width is less than 80 nsec at a charging voltage of 35 kV. FXD patterns of polycrystalline LiF, NaCl, and Si are clearly observed with a focusing method. The diffraction angle can be read to an accuracy of the order of 0.1° around 40° in 2θ.