Tokyo (CNN) A United States citizen could face up to 20 years in jail after trying to board a flight in Japan with a loaded handgun in his luggage.

Michael Edward Applegate, 43, flew from Seattle and arrived with his family at Narita International Airport on Monday, according to the airport police. He was planning to transfer to a domestic flight to Okinawa where he was due to start a new job as a firefighter for the United States Navy.

But when he arrived in Narita -- around 70 kilometers (43 miles) from Tokyo -- airport authorities found he had a Smith & Wesson automatic handgun loaded with 14 bullets, and a magazine loaded with another 14 bullets in his checked luggage.

Applegate confirmed to airport police that the gun was his own, but he said he didn't know why it was there -- and said he had likely packed it as he hurried to prepare for his move, according to the police.

Smith & Wesson handguns are displayed during the 2015 NRA Annual Meeting & Exhibits on April 10, 2015 in Nashville, Tennessee.

The 43-year-old is in custody at the Narita International Airport police station, although he hasn't yet been charged with violating Japan's swords and firearms control law, which imposes an almost blanket ban on citizens owning firearms.

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