A Ground Self-Defense Force major collapsed while visiting a wartime tunnel on Iwojima and later died, the first death on the island since World War II, officials said.
The 45-year-old major was last seen fixing the crumbling entryway to the Senda Bunker while visiting on Thursday, an official from the GSDF Fuji School, where the major was an instructor, said Saturday.
Other instructors, who had walked further into the tunnel, found him slumped on the ground when they returned to the entrance after about an hour, the official said on condition of anonymity, citing department policy.
The island, long called either Iwojima or Iwoto in Japanese, is now officially called Iwoto by the government. It is located in the middle of the Pacific Ocean, about 1,200 km south of Tokyo.
The major was airlifted to a defense hospital in Tokyo where he was pronounced dead, the official said.
He said an autopsy would be held to determine the cause of death, but heat stroke was suspected.
The group was inspecting the wartime facilities before an annual school trip next month to teach war history.
During the Battle of Iwojima in 1945, more than 20,000 Japanese and nearly 7,000 Americans died. Historians say many Japanese soldiers died of heat stroke hiding in the tunnels that were dug to resist a U.S. invasion.