To provide an adjustment technique of ultrasonic beams for detecting the surface of a bone.

A first probe 11 and a second probe 12 are ultrasonic probes for sending/receiving ultrasonic waves relative to the bone. The first probe 11 has a sub array A and a sub array B, and the second probe 12 has a sub array C and a sub array D. The sub arrays A-D form ultrasonic beams respectively. The ultrasonic beams for detecting the bone surface are roughly adjusted by the disposition states of the first probe 11 and the second probe 12 relative to the bone and the ultrasonic beams suited to the detection of the bone surface is finely adjusted by beam forming.

COPYRIGHT: (C)2008,JPO&INPIT