"The Defense Ministry has no concrete plan to introduce THAAD at this stage, but the installation of this kind of new asset can be one of the measures to reinforce our capabilities," Inada said at a press conference on Tuesday, as quoted by the Kyodo news agency.
The Guam system was deployed in 2013 in response to North Korean Hwasong-10 intermediate-range ballistic missile tests.
The THAAD system is designed to intercept short, medium and intermediate ballistic missiles at the terminal incoming stage. The US-South Korean move has been criticized by neighboring China and Russia as inappropriate, possibly disproportionate and affecting other countries' interests.
The situation on the Korean peninsula has become more heated over recent months, with North Korea escalating its ballistic missile and nuclear tests and the United States ramping up its military presence in South Korea.