The present invention is directed to an ultrasound system capable of providing a plurality of M-mode images (431, 432, 433) corresponding to M-mode lines (421, 422, 423) without moving a probe. A volume data forming and reconstructing unit of the present invention forms volume data based on the ultrasound echo signals, the volume data forming and reconstructing unit being configured to determine a beat period of the moving object and reconstruct the volume data based on the beat period. A processor forms a pluraltiy of reference images (410) based on the reconstructed volume data and a plurality of M-mode images (431, 432, 433) each corresponding to an M-mode line (421, 422, 423) respectively set on each of the reference images. A display unit displays the reference images (410), the M-mode lines (421, 422, 423) and the M-mode images (431, 432, 433).
