"To this extent, I am confused over Japan's stance to stay out of the AIIB," Seguchi said, saying that Japan should join the AIIB soon so as to be involved in the mechanism's establishment, rather than complaining as an outsider asking for change.

He said that more than half of the Japanese business circle hope Japan joins the AIIB since its cause to develop the Asian region could boost Japanese companies' performances and Japan's participation will also help the AIIB as a financing screen so as to prevent the AIIB from possible distressed debt in the future, as Japan is a seasoned country when it comes to managing a multilateral development bank.

"The AIIB and Japan could forge a win-win situation for both sides. The success of the AIIB will not only benefit China, but also Japan and the entire region," said Seguchi, who maintains an optimistic attitude toward the China-proposed bank and believes that the AIIB will play a constructive role in improving the regional economy and infrastructural development.

"It is known to all that the Asian Development Bank (ADB) is trapped by its limited financing capability and the United States is opposed to the bank's enlarged scale. Therefore, China proposed the AIIB framework to complement the ADB," Seguchi said, adding "A lot of Asian countries will benefit from the AIIB since they face severe financial deficit in infrastructure construction."

Besides Seguchi, other Japanese economic heavyweights and former senior diplomats also urged Japan to join the AIIB at an early date so as to cooperate with other members to boost regional development.

Former Finance Minister Hisahiro Fujii told Xinhua that the AIIB will play a key role of broad cooperation in the region and it could also serve as a platform for regional countries to develop friendship that could lead to regional peace and prosperity.

Meanwhile, Ukeru Magosaki, former chief of the Intelligence and Analysis Bureau at the Japanese Foreign Ministry, said that the most ideal situation for Japan is to forge interdependent relations with regional countries based on pragmatic interests from cooperation.

To this extent, Japan should be the first to announce its decision to join the AIIB, Magosaki told Xinhua, adding that Japan, right now, missed a good opportunity to join the new initiative and, therefore, it needs to reflect on its miscalculation and make a final decision soon.

Seguchi also said that Japan should make its own decision, although there are pressures exerted on it by the United States.