This paper describes an ultrasonic image synthesis in Fourier transform for visualizing a human brain image under a skull. We employ two ultrasonic array probes with the center frequency of 1.0MHz and 0.5MHz. We perform the experiment with a cow scapula as a skull and a steel sulcus as a lateral cerebral sulcus. We propose two methods to synthesize the ultrasonic data. The first method is a way which synthesized a 1.0MHz data and a 0.5MHz data in the condition of setting a cow scapula and a steel sulcus. The second method is a way, with using the Fourier transform which never changes each frequency component, which synthesized a 1.0MHz data in the condition of setting a cow scapula and a 0.5MHz data in the condition of setting a steel sulcus. As the results, the synthesizing in Fourier transform has higher efficiency than the normal synthesizing on the images for the bone and the sulcus.