This is shitty. I read the Japanese on the site and it seems that if he had been able to prove that he was a political prisoner then he would have been admitted but that would have involved mountains of documents which of course he didn't have on him, and probably a lengthy bureaucratic process.
More evidence of the silly 'sakoku' esque policies that the Japanese government has enacted in the face of a labor shortage. It is also clear that some sort of international crime database must have been referenced in this case unless Japanese intelligence was watching him for some reason.


Japan refuses entry to Antonio (Toni) Negri
The Japanese Ministry of Justice has refused entry to the Italian political philosopher Antonio (Toni) Negri (74) for flimsy reasons. Negri planned at invitation of the International House of Japan from today a lecture tour to the working politics (among other things at the respectable universities of Kyoto and Tokyo). After the Japanese Foreign Ministry had no doubts against Negri's entry, at short notice, nevertheless, the Ministry of Justice responsible for border and immigration regulations of the country expressed doubt. Two days before his departure one demanded of Negri a recorded proof of
his past detention as a "political prisoner".
Japan refuses the entry to foreigners if they served prison sentences of over one year in the past. Excluded by this regulation are political prisoners.
More infos:
http://www.i-house.or.jp/en/ProgramActivities/ushiba/index.htm
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I'm writing to express solidarity with Antonio Negri and distress at the deplorable decision taken by the Japanese Ministry of Justice.
Gayatri Chakravorty Spivak
University Professor, columbia University