A three-dimensional ultrasonic inspection apparatus includes: an ultrasonic transducer disposed m×n piezoelectric vibrators in a matrix; a signal processing device to receive, detect an echo, and generate a three-dimensional image data by processing an electric signal of the echo detected; and a display processing device to display a result of processing the three-dimensional image data generated by the signal processing device, wherein the display processing device includes a peak detecting unit to detect a first peak and a second peak of an intensity distribution of the three-dimensional image data in a depth (z) direction, a joint portion image creation unit to create a three-dimensional image of the joined area by mapping z direction distance of the first peak and the second peak to x-y plane, a determination unit to determine whether the joined area is sound or not, and a display unit to display the three-dimensional image and the determination result of the joined area.