An attachment to a diagnostic ultrasound probe having a beam radiating surface from which ultrasound beam is radiated in a first plane toward a skin surface of an organic body through the attachment which comprises a reservoir section containing acoustic medium. The reservoir section includes an auxiliary membrane, a contact membrane, and a first plane. The auxiliary membrane has an outer surface in contact with the beam radiating surface and is capable of transmitting an ultrasound beam. The contact membrane is arranged to face the auxiliary membrane, has an outer surface in contact with the skin surface of an organic body, and an inner surface, and is capable of transmitting an ultrasound beam. The first wall connects the auxiliary membrane with the contact membrane and has the inner surface crossing the first plane. When an ultrasound beam is radiated from the beam radiating surface and transmitted to the contact membrane, the ultrasound beam is split into a component transmitted through the contact membrane and transferred to the skin surface in the first plane, and the remaining component reflected by the inner surface of the contact membrane. When the remaining component of ultrasound beam is transferred to the first wall in the first plane, a major part of ultrasound beam reflected by the inner surface of the first wall is prevented from being returned to the contact membrane to be reflected by the inner surface thereof, and from being returned to the beam radiating surface.