As shown in FIG., 2(a), according to the present invention, a quartz rod is used where, for example, the diameter of the end on the side to which an ultrasound probe attached is 0.58 mm, the diameter at the narrowest portion is 0.3 mm, the diameter at the end on the specimen side is 0.68 mm, and the length is 38 cm. As a result, the diameter on the side of fused quartz rod 20 to which ultrasound transducer 10 allows a favorable range of L (0,3) mode conversion efficiency; and in addition, the diameter of quartz rod 20 on the side coming into contact with specimen 50 is sufficiently large in comparison with wavelength, and in other portions it is set to be sufficiently narrow in order to obtain flexibility. Fig. 2(b) shows a transmission and a reception waveform.