무권리자에 의하여 등록된 특허발명의 실시에 따른 부당이득반환 의무의 존부

When a patent is filed and registered by a person who is not the rightful owner, and subsequently transferred to the legitimate right holder through a claim for the transfer, the legal effect of the patent is deemed to retroactively apply from the date of registration by the non-entitled person. One of the issues is whether the profits derived from the exploitation of the patented invention during the period of registration by the non-entitled person are subject to restitution as unjust enrichment. Given that the legal effect of the transferred patent retroactively extends to the initial registration date, any economic benefit obtained by the non-entitled person from exploiting the patented invention prior to the transfer may be construed as arising from unauthorized use. Such benefit may, therefore, constitute unjust enrichment of the so-called right infringement-type and be subject to a restitution claim. However, if the non-entitled person was granted a legitimate license to use the invention under a contractual arrangement or similar legal basis, the obligation to return unjust enrichment should be limited to the so-called “excess profit”—that is, the portion exceeding the reasonable return from authorized use. The assessment of excess profit must be based on a comprehensive consideration of various factors that influence the exclusive and monopolistic nature of patent rights. One such factor may include the increase in market share attributable to the exploitation of the patented invention. In contrast, expenses incurred for patent application, registration, and maintenance do not qualify as part of the excess profit derived from the monopolistic and exclusive nature of the patent, and therefore, such costs need not be deducted when determining the amount subject to restitution.