Watanabe, who was born March 5, 1907, previously said he had lived so long because he didn't get angry and tried to keep a smile on his face, the organization said.
He recently had been fighting a fever, stopped eating and began to have a hard time breathing, USA Today reported, citing Japan's Mainichi newspaper.
Officials have not said what caused his death, according to USA Today.
The oldest living woman in the world, 117-year-old Kane Tanaka, also is Japanese, the newspaper reported.
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