Disclosed is an ultrasound apparatus (1000). The ultrasound apparatus includes an ultrasound transceiver that transmits an ultrasound signal to an object and receives an ultrasound echo signal reflected from the object, and a controller that detects a change amount of a diameter of a blood vessel of the object, based on the ultrasound echo signal. The controller calculates a blood pressure graph from the diameter change graph (520), based on an in-systole maximum blood pressure and a diastole blood pressure (e.g. pre-stored). A display unit displays the blood pressure graph and an image representing an inflection point in the blood pressure graph, based on the detected change amount of the diameter. The controller calculates a stiffness of the blood vessel (augmentation index), based on a difference value between a maximum blood pressure in the blood pressure graph and a blood pressure of the inflection point. The ultrasound apparatus may further provide an interface for selecting one from a plurality of pre-calculated inflection points.
