- The man traveled from North Korea across the Sea of Japan by boat
- He said he fled because he was being chased by police
Officials from Yamaguchi Prefecture said the man was interviewed by police, but would not disclose further information to CNN.
According to a report by CNN affiliate NHK, the man traveled from North Korea across the Sea of Japan by boat, saying "the man was drenched (in water) when police took him into custody."
The man, believed to be in his twenties, told police that he left Chongjin, the capital of North Korea's Hamgyong Provice, on Friday night in a wooden boat, broadcaster NHK reported.
He claimed to have jumped from the boat into the sea with a plastic container and drifted to Senzaki by Saturday morning.
The man said he was fleeing North Korea because he was being chased by police after he was caught watching South Korean videos, the Asahi Shimbun newspaper reported.
The man was transferred to Omura Immigration Center in Nagasaki on Sunday, where immigration officials will decide his future based on confirmation of his identity and claims of defection.
South Korea's Foreign Ministry told CNN it was "working to confirm the situation."
In recent years, Japan has seen a number of wooden boats wash up on its shores. Evidence suggests the boats, some of which have contained decomposed bodies, come from North Korea.
But it's not clear whether they were attempted defectors or fishermen who've strayed too far from land.