1. An ultrasound diagnostic apparatus, comprising: a data acquisition section configured to perform transmission and reception of ultrasound with respect to a three-dimensional space including an object tissue to acquire volume data; a representative cross section processing section configured to apply, after a plurality of manual tracing lines are formed on a plurality of representative cross sections which are set with regard to the object tissue, a first correction processing to each manual tracing line; a non-representative cross section processing section configured to form, by interpolation processing based on the plurality of manual tracing lines to which the first correction processing has been applied, respective interpolation tracing lines on each of a plurality of non-representative cross sections which are set with regard to the object tissue, and configured to apply a second correction processing to each interpolation tracing line; and a unit configured to extract object tissue data from the volume data or configured to calculate a volume of the object tissue, based on rows of tracing lines formed of the plurality of manual tracing lines to which the first correction processing has been applied and the plurality of interpolation tracing lines to which the second correction processing has been applied.