1. A diagnosis image generation apparatus comprising: a beamforming coefficient calculation unit configured to calculate a beamforming coefficient to be commonly used in forming low resolution images, wherein the beamforming coefficient is calculated using pixel values forming one of the low resolution images; a low resolution image synthesis unit configured to synthesize each of the low resolution images using the calculated beamforming coefficient; and a high resolution image synthesis unit configured to synthesize a high resolution image using the synthesized low resolution images.