A system using a high-speed and high-precision X-ray inspection system for testing internal short circuits in lithium-ion batteries (LIBs) was firstly developed for the safety test on LIBs. X-ray transmission moving images of the anode and cathode were obtained in the layered LIB structure. The nail-penetration test was chosen to test for the presence of an internal short circuit. This system would allow direct observation of smoke generation inside outside the battery, ballooning of the pouch, as well as changing layered structures of electrodes in real time. Since the results of a conventional nail-penetration test are indicated only by smoke generation, fire, or explosion, this new system allows electrode changes in the pouch to be observed for the first time. This system is expected to lead to great developments in the safety of LIBs.