PURPOSE: To simplify the structure and to obtain an image improved in quality by directing the conical wave front of ultrasonic wave toward a target to be inspected and making inactive an ultrasonic conversion body and a circular plate in the axial direction of an ultrasonic wave deflection element.

CONSTITUTION: An ultrasonic conversion body 1 is mounted on a lens body 2. A connection medium 3 is a connection means for transferring ultrasonic waves 5 to a target 4 to be inspected and a refractive surface 21 is constituted in conical shape. After the ultrasonic waves 5 are reflected by the refractive surface 21, they enter the medium 3. The ultrasonic waves 5 all have the same angle θ for all conical axes 6 and the common wave front is in conical shape. Then, when the angle θ matches a specific surface wave, namely Rayleigh angle for Lamb wave 51, the Lamb wave 51 is excited strongly. The crossing with a surface is in circular shape, the Lamb wave 51 that is a surface wave is propagated in radius direction and focuses an image 52. Also, the Lamb wave 51 tends to leak, namely is strongly reflected into the medium 3, and generates a detectable ultrasonic wave.