In their first deployment overseas in February this year, a group of Raptors on their way to the Kadena airbase on the southern Japanese island of Okinawa were delayed by software problems.
"We understand that the F-22A is an amazing aircraft," the Defence Ministry spokesman said. "Approval would be needed from Congress, and that may be a factor."
U.S. Ambassador to Japan Thomas Schieffer said last week that Europe made good fighter planes, but that interoperability should be a factor in the decision.
"The more interoperability, the greater your ability to have an effect on the battlefield," he told reporters in Tokyo.
Japan and the United States have agreed to step up cooperation between their armed forces in the face of rising regional tensions after North Korea's nuclear and missile tests last year.
The allies are to sign an agreement on the protection of military secrets at a meeting of their respective foreign and defence ministers at the end of April in an effort to enable greater cooperation on missile defence, the Sankei Shimbun daily said on Monday.
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