PURPOSE: To permit accurate evaluation of flaw detecting images by using a digital image memory in the part where flaw detecting image screens are made and accumulated, and using the data of a digital echo memory as a luminance signal.

CONSTITUTION: An A scope signal 100 is subjected to A/D conversion and is stored in an echo memory 14. A deflection circuit 11 makes digital addresses conforming to the loci of ultrasonic waves in accordance with the control of a control circuit 15, and according to said addresses, said circuit writes the data of the memory 14 as a luminance signal into an image memory 12, thereby making and accumulating flaw detecting images such as sectional images or plane images. The accumulated data is read out and is displayed on a display 10. Here, a selecting circuit 13 is provided between the memories 14 and 12, so that the level signal from the memory 14 is written and read out as it is and is supplied to the display 10 without accumulating the same in the memory 12 in the stage of making the flaw detecting images in the memory 12.