Owing to the lack of any introduction and examination to the Theory on Medicial Informed Consent, therefore, this article, firstly, will deal with the background of the formation of the theory and its concept, then, to elaborate, examine the contents and problems of the Informed Consent Theory. Secondly, this article will examine the legal effects of the activities not in conformity with the theory and, for comparison, will introduce some leading cases of informed consent theory in the States and Japan Lastly, the conclusion will compose of the author's and some suggestions as regards the status quo in our legal system.