The purpose of the present invention is to effectively enlarge the coagulation range of a tissue to be treated, by setting the conditions for intermittently providing microwaves. On the basis of a first efficiency (L2) of conduction heating by microwaves with respect to the cumulative emission time of microwaves emitted intermittently to a tissue to be treated (S) and a second efficiency (L1) of conduction heating by microwaves with respect to the cumulative emission time of microwaves emitted continuously to the tissue to be treated, and using as a reference a reference cumulative emission time (Ti1) which is set in advance and serves as a cumulative emission time in which the first efficiency becomes larger than the second efficiency (L2 becomes smaller than L1), an output control section (6) controls a microwave emission section (5) so that microwave emission is carried out intermittently at least after the reference cumulative emission time (Ti1).
