PROBLEM TO BE SOLVED: To set an appropriate visual line direction to a fetus while reducing burdens of a user operation.SOLUTION: An extraction part 30 for amniotic fluid area extracts a plurality of amniotic fluid areas corresponding to amniotic fluid within volume data of a three-dimensional space formed on the basis of reception signals. A specifying part 40 for reference amniotic fluid specifies a reference amniotic fluid area to be a reference of a visual line from the plurality of amniotic fluid areas on the basis of the size of each amniotic fluid area. A direction setting part 50 for visual line sets a visual line direction so as to turn to the fetus through the specified reference amniotic fluid area. A display image formation part 60 forms image data of a three-dimensional display image in which the fetus is projected along the set visual line direction. Thus, while remarkably reducing the burdens of the user operation for setting the visual line direction, the face or the like of the fetus is extremely clearly projected without being hidden by the placenta or the like.
