The patent law sets forth the description requirements on Claims and Specifications, etc. as well as the other patentability requirements such as the industrial applicability, novelty, inventive steps, and first-to-file requirements. Regarding the description requirements (validation of Patent Law section 36), the number of decision of refusal in examination and appeal, decision of invalidation, and actions of annulment of the appeal decision has been increasing. In this study, we analyzed the requirements on definiteness based on recent court decisions and the like in order to avoid such cases that a useful invention to be protected is rejected or invalidated due to inadequate description in claims, so that the invention cannot attain suitable protection as a result of being disadvantaged in patenting and enforcing its right. We found that the Supreme Court has been making different decisions on claims having an expression to specify a product by its production process (product-by-process claims).