1. An ultrasonic diagnostic apparatus comprising: an ultrasonic probe configured to transmit/receive ultrasonic waves to/from an imaging target; an ultrasonic transmission/reception unit configured to make the ultrasonic probe to transmit ultrasonic waves and perform signal processing on the reception signals from the ultrasonic probe; an ultrasonic image constructing unit configured to chronologically construct ultrasonic images of the chronologically measured imaging target, based on the reception signals that are processed in the ultrasonic transmission/reception unit; and a display unit configured to chronologically display the chronologically constructed ultrasonic images, and a control unit configured to control the ultrasonic transmission/reception unit, the ultrasonic image constructing unit and the display unit; further comprising: an operation unit configured to specify a time division of a staining commencement time when a contrast agent enters, for each pixel of the chronologically constructed ultrasonic images; and an image analyzing unit in the control unit configured to determine the color assignment according to the time division of the staining commencement time which is specified by the operation unit, and generate a contrast elasped image by applying a color to the pixel of the ultrasonic images with the determined color assignment.