Two-wave phenomenon, known as the wave propagation of fast and slow waves, has been observed in the cancellous bones when the ultrasonic wave propagates along the trabecular alignment. It is also reported that the acoustical parameters of the fast and slow waves related to not only bone mass but also bone microstructure. In this study, the characteristic refraction of the fast wave was focused, and a method was proposed to estimate the bone microstructure. Cylindrical specimens of cancellous bone were obtained from a bovine femur. Using a conventional ultrasound pulse technique, the receiver was moved to investigate the ultrasonic fields after the propagation in the specimen. In addition, the structure of the specimen was estimated by using the X-ray micro CT. The fast wave showed the “apparent refraction” following the trabecular alignment in the specimen, which was not observed from the slow wave behavior. The ultrasonic field after the sample propagation changed reflecting the trabecular alignment, whi...