Comment on “Maxacalcitol II”: Equivalent Infringement and File Wrapper Estoppel in Japan
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The Doctrine of Equivalents Under Japanese Law
As the Supreme Court sets out in the beginning of its decision, the doctrine of equivalents aims at striking a balance between the proper protection for the invention’s contribution to the state of the art, and legal certainty to third parties.
Among the five criteria set in the “Ball Spline Bearing” decision that courts should apply in order to determine equivalent infringement, there are three positive criteria (i–iii) to be proven by the patentee and two negative criteria (iv and v) to be proven by the alleged infringer.1 The Supreme Court in its decision deals with the fifth requirement, namely that there are no “special circumstances” where, for reasons of equity, a court should deny equivalent infringement. The “Ball Spline Bearing” decision in this connection mentions the “file wrapper estoppel” (where the patentee in the course of the application process disclaims certain features as not falling under the technical scope of the...