1. An ultrasonic diagnostic apparatus comprising: a setting unit which sets, on an ultrasonic image of a heart, a plurality of observation points on conduction pathways of the heart for an electric signal which causes contraction of a cardiac muscle; a tracking unit which tracks each of the observation points to determine a temporal displacement of each of the observation points; a waveform generating unit which generates a plurality of displacement waveforms representing the temporal displacements for the plurality of observation points; and an analyzing unit which analyzes the plurality of displacement waveforms on a common time axis to calculate a time difference of motion for the plurality of observation points.