The US will probably want Japan to adopt the longer term anyway.

So maybe there is not much time left to do this. There is no guarantee that Japan will stay a free country, considering the political climate asking for stronger Japanese IP protection, which has already lead to the IP Basic Law of December 2002.

Article 17 of that law says:

Japan has to put effort into building an internationally harmonized system of intellectual property, working together with the government of each country and under cooperation with the international organizations of intellectual property and other international frameworks. Also, regarding countries or regions where the system for the protection of intellectual property is not sufficiently provided, Japan has to take the necessary legal and other measures for providing an environment where Japanese nationals can acquire and make use of intellectual property rights swiftly and reliably.

Japan might not need much of any pressure to follow the US.

This could be successfull if the movement extend to the majors european countries, Germany, France, Spain, Italy ....

I doubt Japan will be able to withstand U.S. pressure on the question of copyright duration. That's too bad, because if Japan held steadfastly to a life+50 rule it would have not only the moral and intellectual high ground (since life+70 is a ridiculously long term) it would be acting in its own self interest, as well. Japan would be able to make free use of U.S. works for 20 years while Americans would still be paying royalties on Japanese works. This might not make much difference now, but in 40 or 50 years we in the U.S. will still be paying for Rumiko Takahashi's and CLAMP's works (http://www.clamp-net.org) while the Japanese will be able freely to offer, at least among themselves, competing editions and derivations of some American works from the same period.

Sometimes U.S. complaints about Japanese impediments to foreign competition are justified. (Remember a Japanese government minister remarked, some years ago, that Japan could not import some U.S. food products because Japanese intestines are longer than others'; or the controversy over fire blight that seems to have led to the tragic suicide of a Japanese scientist). But U.S. complaints about a shorter Japanese term of copyright would not be justified as long as the Japanese term was reasonably adequate (and the life+50 term is more than adequate) to stabilize the market for new works. After all, it is the copyright monopoly that prevents competitors from offering competing editions of the same work. By holding out for a more reasonable (or less unreasonable) term of copyright, Japan would be encouraging competition, not impeding it.