A downward terrestrial gamma-ray flash (TGF) occurred in association with a lightning discharge in 2017 November 24th. Observations of the downward TGF was made with scintillation detectors located at the Kashiwazaki-Kariwa nuclear power plant in the coastal area of the Japan Sea. Its intensity was so high that the scintillation counters were saturated, and hence the counters failed to correctly detect the downward TGF. After the intense emission of the TGF, high-energy gamma rays lasting for a few hundred ms were successfully observed utilizing the same scintillation counters. A simultaneous detection of neutrons with other scintillation counters was also performed alongside the detection of high-energy gamma rays. The simultaneous detection indicates the occurrence of photonuclear reactions in the lightning.