PROBLEM TO BE SOLVED: To provide an appropriate ultrasonic irradiation apparatus to be used for applying a pre-conditioning method for inducing the stress resistance in a solid organ of a living body.SOLUTION: The ultrasonic irradiation apparatus 10 includes: an ultrasonic transducer 20 for generating ultrasonic waves a casing 30 as a transmission member for transmitting the ultrasonic waves generated in the ultrasonic transducer to an object 70 including a liquid and a cooling part 40 for retaining the temperature of the object at target temperature. Cavitation is generated in the liquid by the irradiation of ultrasonic waves while the temperature of the object is retained at the target temperature by the cooling part, and an activated chemical species produced by the chemical action of the cavitation is loaded onto the object as an oxidation stress.
