A mechanic found the body lying inside the landing gear compartment of the Boeing 777-200 during maintenance after Delta Flight 59 from New York landed at Narita on Sunday night, police official Zenjiro Watanabe said.
The body of the apparent stowaway, identified only as that of a male with dark skin, was clad only in a long-sleeved, plaid shirt and jeans, police at the Narita International Airport said Monday.
"All we know is that he must have sneaked in just before departure, because it is impossible for him to enter the storage during flight," Watanabe said.
The body had no visible injuries except signs of frostbite, and the man might have died of hypothermia during the flight, Watanabe said. The temperature in that part of the plane falls to about minus 58 degrees during flight.
Delta officials were not immediately available for comment, according to the Associated Press.