Article 39 of the Japanese Patent Law is quoted below:
Article 39 (Prior application)
1. Where two or more patent applications claiming identical inventions have been filed on different dates, only the applicant who filed the patent application on the earliest date shall be entitled to obtain a patent for the invention claimed.
2. Where two or more patent applications claiming identical inventions have been filed on the same date, only one applicant, who was selected by consultations between the applicants who filed the said applications, shall be entitled to obtain a patent for the invention claimed. Where no agreement is reached by consultations or consultations are unable to be held, none of the applicants shall be entitled to obtain a patent for the invention claimed.
The patent system grants exclusive rights to the patent holder for a fixed period in return for disclosing the invention. Therefore, dual rights cannot be granted for a single patent. According to Article 39, to exclude duplicated patents, only the earliest patent applicant will be granted a patent if a plurality of patent applications having the same claimed invention is filed.
Determining whether the application was on a different day or the same day, or determining whether the application was earlier, is performed based on the filing date of patent applications that have priority rights claimed. If the patent application is a foreign application, the application filing date is the international filing date. For applications claiming priority rights according to the Paris Convention, inventions described in the patent application that are based on the claim of priority rights are determined based on the date of the first application in a country that is a member of the Paris Convention. For an application claiming priority rights domestically, an invention described in the patent application filed first, based on the claim of domestic priority rights, is determined as having priority, based on the filing date of the first application.
The component elements of the invention claimed in a later application are compared with the component elements of an invention claimed in an earlier application. If they are the same, the later application is rejected. Even when the component elements of the earlier and later patent applications are different, they are determined to be the same under the following conditions.
when the component elements of a later application are known technology
relating to the component elements of the earlier application, or additions, deletions or conversion of the conventional art, and do not provide any new effect;
when the later application is a broader concept of the earlier application that has a narrower concept; and
when the later application and the earlier application are only different in category.