The move will allow the military to defend other nations under what is known as "collective self-defence."
Previous governments have said that Japan's war-renouncing constitution limits the use of force to the defence of Japan.
The constitution was drafted by American occupation forces after World War II in part to prevent a repeat of Japan's invasion and brutal occupation of wide swaths of Asia.
He cites a deteriorating security environment, including China's rise and North Korean missile and nuclear threats.