This paper investigates how Japanese mathematics teachers produce and share didactic knowledge together. It is a case study of a post-lesson reflection meeting so-called "open lesson." The crucial idea of this study is the dialectic between the "specific" and "generic" level of "foci" of the participants' reflections about the observed teaching practice; namely, about applied teacher's specific didactic technique for achieving a specific mathematical goal, and more general pedagogical issues such as realisation of the objectives of mathematics education. This dialectic is mediated by the "meso"-level notion of "mathematical activity," described in the guidelines for Japanese national curriculum. The application of the "scale of levels of didactic co-determination," provided by the "anthropological theory of the didactic" into the analysis shows in what way the dialectic interplay between the teachers' comments with focus of the specific and generic levels influences the development and establishment of the Japanese teachers' shared professional scholarship.