Japan has the National Curriculum and all elementary and secondary schools must do teaching based on text books which speculated by nation. This situation have made most teachers stopped making their lessons based on their own ideas and some devices to facilitate leaning activities. Since 2000 the Ministry of Education has been going on the educational reform. The direction of this reform is to warrant the autonomy of schools and teachers. As the warranted system of teacher's autonomy, all Japanese schools have the continuing professional development system('Kounai-ken') which consists of Jizen-ken, observation lesson, and Jigo-ken. Jizen-ken is to discuss about lesson plan observed by school teachers. Jigo-ken is to discuss about how to improve the observed lesson mainly, and in consequence some teachers learn the new knowledge of teaching, classroom management and so on. The purpose of this study is to explore the function of social interaction among teachers within elementary school in planning the original learning unit in 'Kounai-ken'. The subjects are 4 elementary school teachers charged of 2nd grade and the planned lesson is the subject of life('Seikatu-ka'). The research procedure is 1)to record teachers discussion about lesson plan(Jizen-ken) , 2)to record the lesson by 2 video cameras, 3) to record the teachers discussion about how to improve observed lesson, 4)to make the protocols about Jizen-ken and Jigo-ken, 5)to develop 2 category systems to analyze the protocols, 6)to classify the protocols according to 2 category systems. As the results, 1) there was not always social learning among teachers in Jizen-ken, 2) the leader teacher, who had been studying the subject of life at the city educational research center, conveyed almost information and lesson plan to the other teachers, so that the function of Jizen-ken was to confirm each role of teaching, 3) Jigo-ken was consist of the leader's explaining this lesson and 5 questions and answers. This Kounai-ken did not always serve as the continuing professional development system. This study suggests that this Kounai-ken has two systems for teachers, one is the conveying model and the other is observational learning model. The conveying model is for the leader to give the information and lesson plan like as apprenticeship model. The observational leaning model is to learn something to teach by observing lesson and supplementary questions in Jigo-ken, but this model is not always support each teacher's learning because this learning depends on individual abilities. Kounai-ken is the good system of in- service teacher training for school teachers because this is always based on their own teaching practices, but it does not always serve as In-set in Japanese schools like this school. Finally, some points of improving Kounai-ken are proposed based on this study.