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Q143. Doctrine of equivalence

Q143. Doctrine of equivalence
 Is the doctrine of equivalence available in Japan?

A143. In view of the fact that Japan adopts a statutory law system, and therefore every statute is supreme as the primary legal source. Therefore, the Patent Law Art. 70 is absolute. Judicial judges were hesitant to adopt the doctrine of equivalents to find infringement beyond the letter of a claim. In fact, until 1998 the courts had never held an infringement 57
under the doctrine of equivalents. However, on February 24, 1998, the Supreme Court has provided a guideline in favor of the doctrine of equivalents. Specifically, the following five requirements must be satisfied for successfully asserting the doctrine of equivalents:
1) The part replaced is an insubstantial part of the claimed invention;
2) The replacement of the part achieves the object of the claimed invention and produces the same result as the claimed invention;
3) The replacement of the part would have been obvious to a skilled person at the time of making the accused product (the time of infringement);
4) The accused product was novel and non-obvious at the time when the application was made, which means that the accused product could be patentable; and
5) There is no proof showing that the applicant intentionally excluded the accused product from the claimed invention during the prosecution. This requirement corresponds to the file wrapper estoppels established in the U.S. courts.