With Great Power comes Great Responsibility. What about A. I. Doctor? This book is an introduction to the problems that may arise by using an artificial intelligence program in medical field. A human doctor takes care of the patient's life. Artificial intelligence doctors will also take care of the lives of human patients. Can artificial intelligence doctors be responsible for the patient's life as human physicians? Meanwhile, What is responsibility indeed? Some existence can be responsible? What kind of existence can not be held responsible? This book explores the answers to these questions.