The Korean Supreme Court reversed a lower court decision and remanded the case, holding that the defendant's product, a dried seaweed cutter, included features identical to or equivalent with the claim elements of plaintiff's patented invention ("Patented Invention") and thus infringed upon the plaintiff's patent. (Korean Supreme Court Decision 2013Da14361, July 24, 2014; Korean Supreme Court Decision 2012Hu1132, July 24, 2014).


The Patented Invention covered a dried seaweed cutter that combined the cutting and storing of seaweed into a single process. The dried seaweed cutter has cutting blades laid out in a grid pattern, and seaweed placed on top of the cutting blades is pressed down from above to simultaneously cut the seaweed and store it in a container by sliding down an incline of a grid-patterned box attached to the bottom of the cutting blades.

The defendant manufactured and sold a device with cutting blades, which moved down and cut the seaweed from the top, instead of having the cutting blades underneath the seaweed. The cut seaweed would then be simultaneously cut and stored in a container by sliding down an incline of a grid-patterned box.

Thus, the plaintiff initiated a patent infringement lawsuit seeking injunctive relief against the defendant by asserting that the overall technical features of the two devices were identical except the location of the blade, and that the defendant therefore infringed on the plaintiff's patent under the doctrine of equivalents. Both the first instance court (Seoul Central District Court) and the second instance court (Seoul High Court) dismissed the plaintiff's claim and held that there was no infringement under the doctrine of equivalence, because there was no identity in the principle of resolving the technical problem. The court reasoned that the seaweed cutting feature in the defendant's device differed from that required by the Patented Invention.

[The Plaintiff's Assertions and the Korean Supreme Court's Decision]

On appeal to the Korean Supreme court, the plaintiff asserted that (i) the lower courts adopted an extremely narrow view of the test for the doctrine of equivalents, namely, identity of the principle used to resolve a given problem; and (ii) the determination of whether the "principle used to resolve a problem" is identical should be based on whether the "essence of the technical idea" is identical rather than whether the "characteristic features" are identical.

The Court sided with the plaintiff and held that it is the "essence or core of the technical idea" that should apply when determining whether or not an allegedly infringing product utilizes the same principles as the corresponding patented invention in resolving a given problem. The Court found that the essence of the patented invention was the incline of the grid patterned box that allowed seaweed to be automatically stored after being cut. It was held that the change to the location of the cutting blades was both obvious and easily achieved, and that the changes did not take the accused products outside the scope of the Patented Invention.

As a result, the Court found that the defendant's product infringed upon the plaintiff's patented invention under the doctrine of equivalents.

[Lessons and Implications]

This case is highly significant as it has increased the scope of infringement under the doctrine of equivalents in Korea. This case, therefore, will likely have a significant impact on future patent infringement cases, where infringement under the doctrine of equivalents should always be considered in view of the Supreme Court's clarification of the application of the doctrine of equivalents.