Defense Agency chief Shigeru Ishiba said Thursday "it is worth considering" whether Japan needs an offensive military capability to protect itself from missile strikes.
Ishiba's remarks at the House of Representatives Security Committee are expected to stir controversy amid growing concerns about the North Korean missile threat.
The Self-Defense Forces have no guided missiles to attack overseas military installations, and the Defense Agency has said it would be difficult to launch this type of attack.
But in 1956, the government said in its official view on missile attacks that Japan could attack another country's military bases as an act of self-defense if there were no other means to protect the country.
The Constitution states: "The Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as a means of settling international disputes."
Ishiba told the committee that Japan has never possessed offensive missile capabilities and the government's position is to leave the security of the country to the United States. But he said a move by Japan to develop such an offensive capability would not damage the confidence between Tokyo and Washington.
Ishiba also told the committee of his willingness to introduce a missile defense system to Japan.
"It is the only way to defend against ballistic missiles," he said. "If it is exclusively defense-oriented, I think there is no reason to reject it."
Because the U.S. is planning to deploy its own missile defense system next year, Ishiba said the government should study the details of the system as soon as possible.
Speaking in January to the House of Representatives Budget Committee, Ishiba said that if North Korea threatened to destroy Tokyo and started fueling its missiles, Japan would consider that the beginning of an attack.