The system of opposing a granted patent aims to give a third party the chance to seek an opportunity to file a request with the Japan Patent Office (JPO) to review the appropriateness of the patent.
If an opposition is filed, the JPO examines the appropriateness of the patent and if it finds any deficiency in the patent, it revokes the grant. If the decision of revocation becomes final and binding, the patent is deemed never to have existed from the beginning.
The examination of the opposition is conducted by a documentary examination. In an opposition examination, even grounds that were not initially pleaded by the opponent may be examined, and therefore evidence found by the search conducted ex officio may be used to supplement the evidence that supports the reasons for revocation, including lack of inventiveness or evidence that establishes that the patent has not satisfied the requirements for description and claims.