In recent years, various types of medical applications of microwaves have widely been investigated and reported. In this study, biological tissue coagulation device, which employs the thermal effect of microwave, is introduced. In ad-dition, characteristics of the device are evaluated by numerical calculations based on electromagnetic computation and thermal analysis. Moreover, some experiments using removed organs are also employed. As a result of investiga-tions, possibilities of surgical treatment by developed device could be confirmed.