Local media say a teenaged member of Japan’s Self Defence forces has been arrested in connection with the attack.
The incident took place at a Japanese Self-Defence Forces facility in the city of Gifu on Wednesday.
Two of the injured were in critical condition, according to public broadcaster NHK and other local media.
“Around 9.00am [00:00 GMT] today, there was a shooting incident by a member of the Self-Defence at the… Hino basic firing range and three Self-Defence Force personnel were injured,” top government spokesman Hirokazu Matsuno told reporters.
Matsuno confirmed that a suspect had been arrested but gave no further details.
NHK reported the suspect was a teenage member of the Self-Defence Forces, Japan’s military, and had fired an automatic weapon.
The station also reported that one of those wounded was unresponsive.
Violent crime and shootings are extremely rare in Japan, where gun ownership is tightly regulated, but a number of high-profile recent incidents have raised concern.
In July 2022, former Prime Minister Shinzo Abe was shot on the campaign trail and later died. The man who attacked Abe did so over his alleged links to the Unification Church.
And in April, Prime Minister Fumio Kishida escaped unharmed after a man threw an explosive device towards him at a campaign event.
Security has been tightened in the wake of the incidents, with thousands of police deployed for May’s Group of Seven (G7) summit in Hiroshima.
Last month, police also arrested a man accused of killing four people, including two police officers, in a knife and gun attack in rural Nagano west of Tokyo.