The squad, which will play in pool B of the cup, was named by outgoing Japanese coach Eddie Jones.
Highlanders halfback Fumiaki Tanaka has been picked for the squad and it will be his second World Cup.
Joining him in the squad are hooker Shota Horie, lock Justin Ives and winger Karne Hesketh.
Horie played alongside Tanaka in the Japanese team that played at the World Cup in New Zealand in 2011.
Ives was also selected to play in New Zealand for Japan but picked up a knee injury in a warm up match and never recovered, not playing one minute in the cup in his home country.
Ives, who played for Otago in 2013, has continued to play for the Japanese side and looked a shoo in to play for Japan at this year's cup.
But his selection looked in huge doubt when in a warm up game for Japan against a World XV last month his knee was twisted awkwardly in a ruck and he had to be assisted off the field. The initial fear was his World Cup dream was over but the knee was not significantly damaged and he is right to play in the tournament.
Hesketh has been playing in Japan for five years and made his debut for the test side last year.
Japan has never won a game at the World Cup and is in a pool with South Africa, Samoa, Scotland and the United States.
The side's first match is against South Africa on September 20.
Meanwhile, the international fate of two flankers from the South was set to be known this morning after the Scotland side was named overnight.
Both Scotland and Ireland submitted their squads to World Cup organisers by the August 31 deadline but were not to publicly name them until a day later.
Former Highlanders flanker John Hardie and former Otago loose forward Hugh Blake have both been in the Scotland training squad.
Most pundits felt only one of the two would make the cut, as the experienced Blair Cowan, also a New Zealander, would be the other openside flanker selected.
Japan
Squad
Forwards: Justin Ives, Shoji Ito, Keita Inagaki, Hitoshi Ono, Takeshi Kizu, Hendrik Tui, Luke Thompson, Kensuke Hatakeyama, Michael Broadhurst, Ryu Holani, Shota Horie, Shinya Makabe, Amanaki Mafi, Masataka Mikami, Hiroshi Yamashita, Hiroki Yuhara, Michael Leitch (captain).
Backs: Craig Wing, Kosei Ono, Ayumu Goromaru, Male Sau, Harumichi Tatekawa, Fumiaki Tanaka, Yu Tamura, Toshiaki Hirose, Atsushi Hiwasa, Kenki Fukuoka, Yoshikazu Fujita, Karne Hesketh, Kotaro Matsushima, Akihito Yamada.
