PURPOSE: To detect flaws different in depth, by scanning a focus-type ultrasonic probe in the direction vertical to the surface of a material to be examined.

CONSTITUTION: The center of an ultrasonic beam 2 emitted from a probe 1 in a position A crosses a surface 5a of the material to be examined in a position B, and the angle of incidence of this ultrasonic beam is (i), and the ultrasonic wave is refracted at an angle θ by the surface 5a of the material to be examined and enters into the material 5 to be examined, and the ultrasonic wave is focused in a position C. The probe 1 is raised to a position D which is higher than the position A by a length (h) in the direction vertical to the surface 5a of the material to be examined, and the beam from the probe 1 in the position D is focused at a point G. In this case, the point G is just above a focusing point G0 where the beam is focused when the material 5 to be examined does not exist. Therefoe, the focusing point is moved vertically from the point C to the point G according as the probe 1 is moved vertically from the point A to the point D. Thus, vertical face scanning is possible, and even flaws generated on a vertical plane are detected with a high precision.