Japan - Doctrine of Equivalents interprets Patent Claims

Newsletters and Bulletins / March 1999 / Japan

Japan - Application of Doctrine of Equivalents for Interpreting Patent Claims

In Tsubakimoto Seiko Co. Ltd. v. THK K.K. the Japanese Supreme Court has for the first time accepted the role of the doctrine of equivalents in determining patent infringement. The court noted that it is extremely difficult for a patent applicant to anticipate future developments at the time of originally drafting the claims and that patents should therefore be construed to cover alleged infringements that use "substantially the same elements" as the patent claims. It listed five factors to be considered in determining whether something falling outside the literal wording of the claims could be an infringement:

1. the differing element should not be an essential part of the patented invention;

2. the alleged infringement with the differing element should achieve the same object and effects as the patented invention;

3. at the time of production of the alleged infringement one skilled in the art would have been able to make the change easily (i.e. the change was an obvious variant);

4. the alleged infringement is not itself part of the prior art or obvious in view of it; and

5. no special circumstances preclude a finding of infringement, such as the applicants having excluded the alleged infringement from its scope of protection during prosecution of the application giving rise to the patent in suit.

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