A three-dimensional ultrasonic inspection apparatus 10 can make increased inspection accuracy in comparison to the conventional apparatus and includes: an ultrasonic transducer 11 disposed m×n piezoelectric vibrators in a matrix; a signal processing unit 17 to receive, detect an echo, and generate a three-dimensional image data by processing an electric signal of the echo detected; a peak detecting element 51, 52 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 36 to create a three-dimensional image of the joined area 15 by mapping z direction distance of the first peak and the second peak to x-y plane; a determination unit 37 to determine whether the joined area 15 is sound by two-step determination; and a display unit 38 to display the three-dimensional image and the determination result, of the joined area 15.