Finally, on Sunday, a Japanese military vessel spotted the 60-year-old waving a red cloth. He was about 15 kilometers (about 10 miles) offshore from the earthquake-ravaged city of Minamisoma, said Yoshiyuki Kotake, a Defense Ministry spokesman.
Shinkawa told his rescuers that the tsunami hit as he and his wife returned home to gather some belongings after Friday's quake. His wife was swept away, Kotake said.
"Several helicopters and ships passed by, but none of them noticed me," he was quoted by another defense agency spokesman, who refused to be identified by name, as saying.
Japanese troops used a small boat to pluck him from the ocean.
Military officials said Shinkawa was lucky that mild weather and relatively calm seas enabled him to stay afloat for nearly two days, the Kyodo news agency reported.
"I thought today was the last day of my life," it quoted him as saying.
For emergency information, assistance, and locating family in connection with earthquake in Japan: http://www.facebook.com/l/6b2e3a9CLMNbUwBsOw1jOL8d5aw/www.jhelp.com
Phone numbers in US and Japan:
202 559 4683
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011 81 90 7170 4769
011 81 90 3080 6711