>From the JPO web stie:
"Any person may file an opposition to the grant of a patent within six
months of the publication of the Patent Gazette in which the granted
patent appears.:
Note that registration precedes publication by about two
months.
Oppositions can be search in Japanese in the PATOLIS
database.
-- Alan Engel ISTA, Inc. ConvertedKokai(tm) machine translations of Japanese patents http://www.intlscience.com