Abstract: An ultrasonic-wave irradiation unit capable of reducing erosion and cleaning unevenness on a diaphragm and improving the joining strength of an ultrasonic transducer to the diaphragm includes a diaphragm, an ultrasonic transducer, a front-side resonating member, and a rear-side resonating member. A stud bolt protrudes from the non-radiation surface of the diaphragm. The transducer front plate of the ultrasonic transducer is joined to the non-radiation surface. The front-side resonating member is joined to the non-radiation surface and the bolt is inserted therethrough. The rear-side resonating member is provided at the tip of the bolt to fasten and secure the front-side resonating member. End-positioned resonators, mid-positioned resonators, and the ultrasonic transducer are arranged in a column. The rear-side resonating member of the end-positioned resonator is formed from a metal material with higher bending rigidity than the front-side resonating member.