An ultrasonic system is good for the evaluation of children because its noninvasiveness. The ultrasonic bone measurement system LD-100 has been developed on the basis of the principle of the fast and slow wave phenomenon in the wrist bone. In the measurement of small bones such as those of children, there are some problems due to the influences of circumferential waves on the fast and slow waves. When the diameters of the focused transducers were small, the appearance of the circumferential wave around the cortical bone became late, and it could avoid one of the influences of the circumferential waves. (C) 2014 The Japan Society of Applied Physics