In a recent case (2017Hu479, rendered on 22 December 2017) the Supreme Court clarified and substantially broadened the scope of the doctrine of equivalents as applied in patent infringement cases in South Korea.


The patent at issue (KR 10-892615) related to a device for lifting a 'gang form' – a type of external scaffolding used in construction to allow the building of high walls in stages. A gang form is used to support a section of wall, and once the wall is set, a crane is used to lift the gang form by means of a lifting loop attached to the top of it, thus allowing another section of wall to be built on top of the previous one.

The patent specifically related to a safety device used to lift the gang form. The invention involved a second safety loop slightly offset from the lifting loop, such that the safety loop could be lifted some distance before the lifting loop was also engaged. Lifting the safety loop would lift a cover covering bolts in the wall section that could be disengaged before the lifting loop was engaged by the crane hook and the entire gang form was lifted. Since the bolt cover kept the bolts from being accessible before the safety loop was engaged to lift the bolt cover, the invention prevented the risk of the gang form collapsing due to premature loosening of the bolts before the crane had engaged the gang form.

The defendant's non-infringement argument pointed to the lack of a 'guiding element' in the accused product. Such an element in the invention served to keep a safety loop in position while being lifted but before the lifting loop was also lifted. The argument also cited the specific type of spring used to lift the bolt cover. While the patent claim did not specify the structure of the guiding element, the specification disclosed as examples tube-like structures through which the safety loop was inserted. While the accused product did not contain any tube-like structures corresponding to the example guiding elements in the patent, there were other structural elements that served to maintain the position of the safety loop while being lifted. Further, the claim cited a compression spring for lifting the bolt cover, while the accused product used a torsional spring for this purpose. At the first and second instances, the lower courts determined that the patent was not literally infringed and that the doctrine of equivalents did not apply because:

  • no element of the accused product was directly substituted for the tube-like guiding element in the patent; and
  • different types of spring were used.

Supreme Court decision

The Supreme Court reversed, citing its earlier decision in a doctrine of equivalents case involving an invention for cutting roasted laver (2012Hu1132, rendered on 24 July 2014). The Supreme Court determined that the Patent Court (the appellate court) had misinterpreted the scope of the claimed invention and had misapplied the doctrine of equivalents in this case by focusing only on the differences in structure without a full consideration of the essential purposes and problem-solving principles of the invention and accused product. The Supreme Court held that 'guiding element' and 'compression spring' were too narrowly limited to the specific structures exemplified in the specification, and that the accused product had infringed under the doctrine of equivalents because there were other structures in the accused product that could serve the same function as the claimed elements, while any differences in structure were not unexpectedly unconventional and did not provide any different effects from the patented invention.

The Supreme Court noted that its earlier decision had been too narrowly interpreted by lower courts and indicated its intention to clarify again the proper application of the doctrine of equivalents. The Supreme Court appears to have essentially broadened the doctrine to emphasise that structures in an accused product that are very different from claimed elements can still be 'equivalent' provided that the differences are conventional and the basic purpose of the invention is still achieved.

For further information on this topic please contact Youngsun You, Inchan Andrew Kwon or Woo Seok Kim at Kim & Chang by telephone (+82 2 3703 1114) or email (, or The Kim & Chang website can be accessed at

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