To evaluate the X-ray-induced afterglow phenomenon, we developed an ionizing-radiation-induced luminescence characterization system equipped with a pulse-width-tunable X-ray source. The system consists of a pulse X-ray tube and a detector system based on photon counting. The excitation pulse width was tunable from nano-to millisecond ranges, and the dynamic range of the X-ray-induced afterglow was 106. Conventional scintillators for X-ray CT or security systems, namely, Bi4Ge3O12, CdWO4, Tl-doped CsI, and Tb and Pr-codoped Gd2O 2S, were evaluated for the performance test. Results show that the afterglow time profiles of these scintillators are consistent with generally known results with high accuracy.