According to an embodiment, an ultrasonic flaw detection device is provided with: an ultrasonic probe, which applies ultrasonic waves, by driving a plurality of ultrasonic elements, to a test object to be inspected, and which receives reflected ultrasonic waves from the test object; and an analysis unit, which analyzes the signals of the reflected ultrasonic waves received by the ultrasonic probe, and which calculates the flaw detection results. The analysis unit calculates the flaw detection results using an ultrasonic wave propagation path obtained on the basis of the surface information of the test object having the ultrasonic waves applied thereto, thereby obtaining highly accurate detection results even the surface of the test object is formed in complex shape.