This ultrasonic wave irradiation device is provided with: a therapeutic ultrasonic wave emission unit (15) for emitting a pulsed ultrasonic wave a monitoring-use ultrasonic wave emission unit (16) for ascertaining an administration site where a mixture of a drug and an ultrasound contrast agent has been administered a control unit (19) for controlling the therapeutic ultrasonic wave emission unit so that the focus position of the therapeutic ultrasonic wave is moved across the entire area where the drug should be distributed starting from the administration site of the mixture of the drug and the ultrasound contrast agent and a brightness change monitoring unit (23) with respect to the brightness of an ultrasonic echo signal. Therapeutic ultrasonic wave irradiation is carried out while the output of the brightness change monitoring unit (23) is used to check whether or not ultrasonic wave irradiation is sufficient at each focus position.
