the present invention provides a method for ultrasonic measurement of mainly the depth of a flaw possibly existent in a solid mass and opening to the surface of the solid mass . an ultrasonic wave is transmitted into the solid mass by scanning an ultrasonic probe back and forth on the surface of the solid mass with respect to a flaw in the solid mass , a threshold of a predetermined level is set for a curve defined by levels of echoes of the ultrasonic waves reflected from the flaw according to the position of probe , the area under the curve and above the threshold is integrated for the range of movement of the probe , and the depth of the surface opening flaw is measured using as an evaluation index the value of the integrated area of the area . the method according to the present invention is applicable to nondestructive , easy , accurate and realtime measurement of the depth of weld cracking in a welded portion , fatigue cracks in a stress - concentrated portion of members of a machine , etc .