Police discovered a wooden ship carrying the corpses of seven men on a beach in Ishikawa prefecture last week.
Inside the boat they also found a badge with the likenesses of North Korean leaders Kim Jong Il and Kim Il Sung, along with a cigarette box with Korean letters, officials said.
The ship found in Ishikawa was the first in 2018 found carrying dead bodies, though eight other vessels have also washed up.
On the same day, a man's body was also found on the same beach, about 15 meters away from the boat.