Australian Foreign Minister Stephen Smith on Thursday said he was not surprised with the news that outgoing Defense Minister John Faulkner has been contemplating leaving cabinet for "quite some time."

Senator Faulkner on Wednesday denied that his decision to quit the ministry after the next election was due to Labor's dumping of Kevin Rudd as prime minister.

Opposition Leader Tony Abbott said the defense minister's move was "an implicit vote of no confidence" in the new Prime Minister Julia Gillard's government.

But Smith denied that was the case. He said Senator Faulkner would be missed "but from my perspective it's no surprise."

"I know him well and I know this is something that he's been contemplating for some time," Smith told ABC Radio.

"It's quite clear that John has continued to perform roles for us out of his duty and his obligation and his adherence to conducting himself honorably, rather than doing that which he would personally prefer."

Faulkner on Wednesday announced that he will quit his portfolio after the next federal election.

Faulkner said his move was not because Kevin Rudd was dumped as prime minister last month, rather his decision was motivated by the need for "generational change."