1. An ultrasound diagnostic apparatus comprising: an ultrasound transceiving unit that transmits ultrasound waves toward a subject to be examined into which a puncture tool is inserted, receives reflected waves of the ultrasound waves reflected from the subject and the puncture tool, and generates echo signals of time-sequential frames based on the received reflected waves; an ultrasound image generation unit that generates an ultrasound image of the subject based on the echo signals generated by the ultrasound transceiving unit; an image display unit that displays the ultrasound image generated by the ultrasound image generation unit; a differential echo signal generation unit that generates a differential echo signal between time-sequential frames from the echo signals of the time-sequential frames; a tip candidate detection unit that performs a tip detection process based on the differential echo signal generated by the differential echo signal generation unit to thereby detect at least one tip candidate including a tip end of the puncture tool; and a tip candidate processing unit that highlights a tip candidate of the puncture tool detected by the tip candidate detection unit to thereby generate a tip image in which one or more tip candidates of the puncture tool are highlighted, wherein the image display unit displays the tip image of the puncture tool highlighted by the tip candidate processing unit so as to be superimposed on the ultrasound image generated by the ultrasound image generation unit.