PROBLEM TO BE SOLVED: To improve accuracy and resolution performance in an automated discrimination between a treated region and an untreated region by HIFU (High Intensity Focused Ultrasound) treatment.SOLUTION: A therapeutic effect decision part 25d analyzes the signal intensity of a blood flow in a treatment ultrasound converging region and its peripheral region before and after ultrasound irradiation, so that a region where its signal intensity 511 after the ultrasound irradiation continues to be lower than the lower limit of a set range 510 is decided to be a treated region A, while a region where its signal intensity 513 continues to be higher than the higher limit of the set range is decided to be an untreated region C, and a region where the variation pattern of its signal intensity 512 does not belong to either the treated region or the untreated region is decided to be an uncertain region B. With respect to the uncertain region B, the temperatures of the treatment ultrasound converging region and its peripheral region before and after the ultrasound irradiation are analyzed, so that a region where the temperature of each part in the uncertain region B is equal to or more than a predetermined temperature threshold 611 is decided to be a treated region B1 and a region where the temperature is less than the temperature threshold is decided to be an untreated region B2.
