This paper describes a data synthesis method of two ultrasonic waves for visualizing brain image under skull. In it, we employ 0.5MHz and 1.0MHz ultrasonic array probes. We synthesize the waves of 0.5MHz and 1.0MHz and visualize the sulcus and skull. We perform the experiment with a cow scapula as a skull and a steel sulcus as a cerebral sulcus. We calculate the thickness of the bone from the synthesized waves. The thickness is determined from the surface and bottom points determined from the wave. The surface point is easily determined from the wave. The bottom point is determined by fuzzy inference. The sulcus surface was extracted from a B-mode image made from the synthesized waves. As the result, we successfully determined the skull depth and visualized the sulcus from the synthesized waves in comparison to the results obtained from each waves of 0.5MHz or 1.0MHz.