The purpose of this study is to explicate the nature of discovery learning in the light of the idea of Bruner\'s. Generally speaking, discovery learning is defined as a model of instruction for students to discovery the principle hidden in the facts. The general definition on discovery learning gives us a important suggestion that principle as a content of the school subjects is distinguished from facts. But the definition is able to misguide us to the sense that the teacher does not teach, and the students find out everything for themselves in discovery learning. Of course, no sane person supposes that students are going to discover the whole of what they need to know quite apart from the teacher\'s activity. We are able to correct the misunderstanding with Bruner\'s idea on discovery learning. First of all, Bruner makes clear the nature of school subjects implied in the general definition with the concept \'structure of knowledge\' and \'middle language\'. This nature states that the structure of knowledge in upper layer contains middle languages in the lower layer as whole without distinctions. Following the statement, Bruner\'s idea on discovery learning is conceptualized as a method of teaching that students comes to possess the structure of knowledge through the middle language. It is necessary the teacher\'s activity for students to realize the idea of discovery learning. Teacher guides the experience of jumping from the middle language which lie in the lower layer to the structure of knowledge which constitutes the upper layer of school subjects by the subtle use of language. Students become to possess the structure of knowledge only by the teacher\'s activity.