The luminal surface of the arterial wall roughens in the early-stage atherosclerosis. A possible differentiation between the reflected and scattered components in the ultrasonic echo from the arterial wall potentially can serve as a diagnostic tool when such roughening occurs. This study presents a method for the differentiation of reflection and scattering components by creating ultrasonic beams from different directions using the synthetic aperture method. The technique was evaluated in experiments on urethane rubber phantoms. The average magnitude of the echo signals from each phantom and the ratio of the mean values of the reflection and scattering components were found to be proportional to the arithmetic average roughness evaluated with a laser surface profilometer. These results show that the proposed separation technique has potentials in evaluation of surface roughness.