PURPOSE: To securely detect whether or not there is a defect in a body to be inspected by emitting ultrasonic pulses at right angles to the surface of the body to be inspected and extracting echoes reflected by the top surface and bottom surface.

CONSTITUTION: Ultrasonic pulses P from a probe 12 are radiated to the surface S of a fuel coated pipe 1 at right angles, the probe 12 catches the surface echo SP reflected by the surface S of the fuel coated pipe 1 and the bottom surface echo BP1 reflected by the bottom surface B, and those surface echo SP and bottom surface echo BP1 are passed through a surface echo extraction gate and a bottom surface echo extraction gate to accurately extract a surface echo signal and a bottom surface echo signal. If there is a defect present in this pipe 1, the majority of the ultrasonic wave pulses P are diffused and reflected by the defect part F to attenuate. The remainder passes through the defect part F to return to the probe. Thus, the echoes reflected by the top surface and bottom surface are extracted to easily and securely detect whether or not there is the defect in the inspected body.