This study was conducted to obtain fundamental data on the sympathetic detonation of steel shells with confined explosive for the safe treatment of munitions. In the study, we performed experiments on sympathetic detonation using steel shells with confined explosive and took high-speed framing photographs of the explosion and sympathetic detonation processes. The photographs obtained showed that the target steel shell for sympathetic detonation (the acceptor), which was placed 60 mm apart from the initiating steel shell (the donor) in series, was induced to explode by the effect of the explosion of the donor shell, indicating that shock waves generated by the impact of fragments of the donor shell initiated a chemical reaction or detonation in the neighboring acceptor shell. Whether or not the test shell was induced to detonate is considered to be strongly related to both the geometric configuration of each steel shell and the intensity of explosion of the initiating steel shell. Initial changes in the shape of the donor shell at the time of explosion were clearly observed, and the displacement of the outer wall of the shell increased with time. The temporal changes in displacement thus revealed the time-dependent acceleration processes of the outer wall. Assuming that the expansion velocity was constant, the estimated velocity was about 0.8 km·s-1 in the delay time range of 0 to 170μs after initiation of the donor. The measured terminal velocity of the fragments was found to be in the range of 0.7 to 1.3 km·s-1 in the delay time range of 2 to 12 ms. These results showed good agreement with the numerical results calculated by AUTODYN-2D.