A modulation frequency control unit (36) controls a displacement-use transmission unit (34) such that displacement-use ultrasonic beam (EB) is subjected to modulation processing using a relatively high modulation frequency and a relatively low modulation frequency. A displacement measurement unit (24) measures the displacement of a tissue in a treatment area (P) at each of the modulation frequencies, and a coagulation measurement unit (25) measures local coagulation in the treatment area (P) on the basis of the measurement result of the displacement at the relatively high modulation frequency, and measures wide-area coagulation in the treatment area (P) on the basis of the measurement result of the displacement at the relatively low modulation frequency. Consequently, for example, the presence or absence of local coagulation immediately after coagulation has occurred, and the like, can be measured with high accuracy, and further, for example, the size of wide-area coagulation after coagulation has progressed, and the like, can be measured with high accuracy.