Abstract: A probe has a step portion between its upper and lower lateral faces. A water bag has a container portion for containing water therein, and an engaging portion which is integrally formed with the container portion and which has a greater wall thickness than that of the container portion. The engaging portion is put on the upper lateral faces of the probe, with its sealing portion being pressed against the step portion. The press portion of a fitting member is caused to engage with the step portion, with the sealing portion therebetween. In this state, a clamp member clamps the fitting member, so that the sealing portion is held under pressure between the press portion and the step portion. Thus, the sealing portion is pressed against the step portion, and water poured into the water bag through a tube is contained therein in a liquid-tight manner. The probe and the object to be examined are acoustically coupled by means of the water.