An ultrasonic irradiation apparatus irradiates ultrasonic waves onto a wide area having three-dimensionally curved surfaces. An ultrasonic irradiator having a plurality of ultrasonic transducer is arranged in a plane. The position of at least a portion of the ultrasonic transducers is mutually and flexibly changeable in three dimensions. Ultrasonic transducers are installed on a surface of a flexible and/or elastic sheet member or net member. The ultrasonic irradiator may include a plurality of ultrasonic transducers formed on a flexible piezoelectric sheet member, including driving electrodes arranged on one surface and opposed electrodes arranged on another surface. The ultrasonic irradiator may be installed on or inside of a flexible planar bag containing a fluidic ultrasonic conductive medium. A mechanism is provided for moving or tilting the ultrasonic irradiator with respect to the object, or a band-holding member may be provided for fitting the irradiator to the object.