Vacuum ultraviolet (VUV) and soft X-ray measurements are important means of diagnosing impurities in magnetically confined plasmas used in fusion research. Recently, space- and time-resolving flat-field VUV (150–1050 Å) and soft X-ray (20–350 Å) spectrographs have been constructed by using aberration-corrected concave gratings with varied-spacing grooves which give a wide simultaneous spectral coverage on a microchannel-plate intensified detector. Calibration experiments have been performed at beamlines 11A and 11C at the Photon Factory of the High Energy Accelerator Research Organization. The relative efficiency of the VUV spectrograph has been measured for P-polarization geometry in the spectrograph. In the soft X-ray spectrograph, efficiencies have been obtained for several different points of irradiation on the grating along the groove direction and for two (S and P) polarization geometries.