In the recent case of THK Co Ltd v. Tsubakimoto Precision Products Co Ltd the Tokyo High Court addressed the issue of the proper scope of claims in Japan. Traditionally claims in Japan have been construed literally and sometimes even as being confined to the specific embodiments described (although the latter practice is sometimes justified as a means for interpreting the claims so as to maintain their validity when there is close prior art). A decade or so ago there was a brief period when the Osaka court seemed ready to construe claims more liberally, but this period ended with the retirement of the judge who had been the prime mover for liberal construction. Now the Tokyo High Court has taken a step in this direction.

In the THK case after asserting that in general claims should be construed fairly strictly so as to ensure legal certainty, the court indicated that there could be exceptions to this general rule if three conditions were met: 1) the alleged infringement and the claimed invention solve the same problem by using the same basic technical idea, 2) no significant effects arise from the differences between what is claimed and the alleged infringement and 3) given the state of the art at the time of filing of the application giving rise to the patent in suit, one skilled in the art would have no difficulty with the substitution of a feature of the alleged infringement for a feature of the invention as claimed.

A subsequent decision of the Osaka High Court in Genentech Inc. v. Sumitomo Pharmaceuticals Company Ltd. indicates that this court too may take a slightly broader view of what is protected by a patent claim than just the strict literal wording. In its view, something falling outside the literal wording of a claim may be an infringement if (1) it substitutes an element of what is claimed by something that is interchangeable with it and causes no significant change in the nature of the product and (2) there was no difficulty in making the interchange.