An extraction period specification unit specifies an extraction period (extraction section) for an M-mode image. A model expansion/contraction unit establishes a contour model (initial configuration) in relation to the specified extraction period while expanding/contracting the contour model in the direction of the time axis so as to conform with the extraction period. A node position change unit performs, for each node forming a plurality of node strings included in the established contour model, an edge (contour) search while successively changing the positions of the nodes, resulting in the formation of a revised contour model comprising a plurality of nodes at an edge detection position. A trace unit carries out interpolation on a plurality of node strings included in the revised contour model, thereby generating a plurality of trace lines simulating a plurality of contour lines.
