The Bank of Japan is still too optimistic about the time needed to achieve its 2 percent inflation target, given the country's entrenched deflationary mindset, a former BOJ executive director said.

Any lack of progress toward that goal, though, is unlikely to trigger additional easing by the central bank because it has already adopted the strongest possible policy measures, said Kazuo Momma, an economist at Mizuho Research Institute who left the central bank in May.

Further easing is "not needed at all, not at all," in the foreseeable future, he said in an interview with Bloomberg on Tuesday in Tokyo.