The Doctrine of Equivalents (DOE) in Korea

The rationales of the doctrine of equivalents in Korea are basically similar to those of the U.S. Namely, when an accused product or process performs substantially the same function in substantially the same way to obtain the substantially same result of the patented invention, the accused product or process infringes the patent right. 

In particular, the Korean Supreme Court held that the accused product or process infringes a patent where an element of the patented invention is substituted with another element and, if (i) the technical concepts or principle to solve the objective of the patented invention and the accused invention are the same or common; (ii) the substituted element in the accused invention performs substantially the same function in substantially the same way to obtain the substantially same result of the patented invention; (iii) such substitution is obvious to an ordinarily skilled person in the art. However, the doctrine of equivalents shall not be applicable to the circumstances that (iv) the accused substitution was already known to skilled persons in the art at the time of filing an application and (v) the accused element was excluded from the claimed invention during prosecution. 

On July 24, 2014, the Supreme Court further clarified the scope and meaning of the above (1) requirement of DOE; the technical concepts or principle to solve the objective of the patented invention and the accused invention must be the same or common. 

The patent claimed a cutter for dry seaweed. The seaweed cutter has cutting blades laid out in a grid pattern. Seaweed is placed on top of the cutting blades and pressed from top to down and then sliding down into a container through a grid-patterned box attached to the bottom of the cutting blades. The patented invention can achieve a cutting and storing of seaweed in a single process.

The accused cutter is different from the patented cutter in which the accused cutter has moving blades that move from top to down and cut seaweed. Instead, the patented invention does not have moving blades. Except the position of blades, other technical features of the two devices are the same. Two cutters perform the same function in the substantially same way and achieve the same result. 

However, the Seoul High Court denied patent infringement under DOE because the accused cutter did not meet the (1) requirement of DOE. The accused cutter cut seaweed in a different way from the patent technology; there is no the same technical principle of resolving the technical problem. 

The Supreme Court vacated the lower court decision. The Court held that the "essence or core of the technical idea" must be determined between two cutters in order to apply DOE and then found that two cutters used the same technical idea because it should be the incline of the grid patterned box that allowed seaweed to be automatically stored after being cut and it is found in two cutters although two cutters employed different embodiments. The Court found that the change to position of the cutting blades was obvious. The Supreme Court decision clarified (1) requirements of DOE under the Korean patent law. In practice, patentees may have higher chance to apply DOE under the recent decision.