Japanese Unity of Invention Requirement

What is unity of invention in general?

Unity of invention relates to the concept of one invention in one patent application. In most jurisdictions, in order to include two or more inventions in one application, the inventions as defined in the claims must be linked by a general inventive concept by sharing the same (identical) or corresponding (achieving the same technical effect, solving the same technical problem, or having an interrelated relationship) special technical features (STFs). In Europe, among other jurisdictions, a STF refers to a feature that patentably distinguishes a claim over the prior art. 

How to overcome a rejection for lack of unity of invention in general?

In most jurisdictions, where two or more independent claims are included in one application, an examiner determines whether the independent claims share a same or corresponding STF based on the prior art search conducted. If the independent claims do not share a same or corresponding STF, the examiner will issue a rejection for lack of unity of invention. Applicants may amend the independent claims to make the claims share the same or corresponding STF to overcome the rejection, argue against the rejection, or select an independent claim set to prosecute.

What is special about the Japanese unity of invention requirement?

While Japanese patent law also allows two or more inventions to be included in one application if they share a same or corresponding STF, the Japanese Patent Office (“JPO”) approaches this issue very differently. If the claims, including independent and dependent claims, do not share a same or corresponding STF, the claims will be found to lack unity. This may occur even if the claims of an application include only one independent claim.

Under Japanese patent law, STF is defined as a contribution that the invention makes over the prior art. However, Japanese patent law is not clear about how a STF is determined. For example, a STF is not necessarily a feature that can patentably distinguish a claim over prior art. Rather, the existence of a STF is determined based on the entire disclosure of the application and common general knowledge.

According to Japanese Patent Examination Guidelines, “[i]n cases where the invention first described in the claims has no special technical feature, it is determined whether there are inventions claimed in the same category that include all matters specifying the invention of Claim 1. In cases there are such inventions, it is determined whether the invention of the claim to which the smallest claim number is attached has any special technical feature.”

In other words, if the claims of an application include more than one STF, the one included in the claim that has the smallest claim number will be determined to be the STF for determining unity of invention. 

Once a STF is determined, the examiner determines the claims to be examined based on the STF and examination efficiency. Claims reciting the same or corresponding STF will be examined. Claims reciting features technically related to the problem solved by the determined STF will also be examined for examination efficiency. The other claims will not be examined. 

Once the STF and the claims to be examined are determined by the JPO, applicants cannot amend the claims to change the STF that has been determined by the examiners.

In what circumstance do claims fail to fulfill the Japanese unity of invention requirement?

A common situation is where the invention defined in Claim 1 is broad and lacks novelty and inventive steps based on the prior art, and dependent claims that depend on Claim 1 define various embodiments/configurations. As searching prior art for every embodiment and configuration will be burdensome to the examiners, Japan examiners are more likely to issue a rejection for lack of unity in this situation and restrict the claims to only one invention, i.e., the claims that include the STF determined by Japan examiners.

This can be analogized to a situation where U.S. examiners issue a restriction/election requirement asking applicants to elect a particular grouping of claims among multiple perceived species for efficiency of examination. However, unlike the U.S.’s restriction/election requirement, the JPO unity of invention requirement does not give applicants an opportunity to “elect” the desired embodiment/species for examination. Instead, the JPO will elect the embodiment/species for applicants based on the determined STF. Applicants cannot amend the claims to add features relating to non-elected species. This can be detrimental to applications.


In an application where only one embodiment is described in the specification and the independent claim(s) and the dependent claims are related to the same embodiment, the claims should fulfill the unity of invention requirement because all features recited in the claims relate to one single embodiment that can solve the same prior art problem or achieve the same technical effect.

However, where an application includes multiple embodiments and the claims define multiple embodiments or configurations, a rejection for lack of unity is likely even if the claims include only one independent claim. If you have any questions related to this topic, please contact Li-Hua Weng at lihua@burrisiplaw.com.