An ultrasonic diagnostic system according to the present invention has an ultrasonic transducer mounted on a catheter, an instantaneous distortion value calculator which calculates an instantaneous distortion value at the location to be evaluated in the blood vessel based on received signal representative of received reflection by the ultrasonic transducer, an analyzer which analyzes a state of the location to be evaluated using time-series data of instantaneous distortion values which are calculated at a plurality of times in a chronological sequence by the distortion value calculator, and a display which displays an analyzed result produced by the analyzer.