The artificial endocrine pancreas is a feedback controlled instrument regulating insulin delivery on a minute-by-minute basis according to measured blood glucose levels. It has been proven to be useful not only as the therapeutic tool of diabetes mellitus but also as an elegant research tool for investigating the pathophysiology of the disease. The wearable type of closed-loop system has been developed recently for the first time by the authors. The breakthrough is the establishment of needle-type glucose sensor. The trend in development of closed-loop glycemic control system which enables perfectly physiological regulation on long-term basis, is directed to implantable devices. Much efforts have been conducted now to realize these devices.