Michael Edward Applegate, 43, flew from Seattle and arrived with his family at Narita International Airport on Monday, according to the airport police. He planned to go on an internal flight to Okinawa, where he had to start a new job as a firefighter for the US Navy.
But when he arrived in Narita, about 70 miles (43 miles) from Tokyo, the airport authorities found that he had an automatic pistol Smith & Wesson loaded with 14 bullets and a magazine loaded with another 14 cartridges in his check luggage.
Applegate confirmed to the airport police that his pistol was his but he said he was not I do not know why he was there – and he said he probably packed him because he hurried to prepare for his move, according to the police.
The 43-year-old is detained at Narita International Airport police station, although he has not yet been accused of violating the Japanese sword and the firearms control law, which imposes an almost complete ban on citizens owning firearms.
If he is charged and found guilty, he faces a jail sentence of at least three years and a maximum of 20 years.
Under Japanese law, weapons and bullets should be kept separate. As Applegate's weapon was loaded, its actions would be considered particularly serious.
CNN reaches the US Transportation Security Administration (TSA) for comment.
At that time, the Japanese Ministry of Transport said there would be no sanctions for Delta Air Lines or TSA. But that was the responsibility of TSA and asked the organization to take preventive measures.