Provided is a method of outputting a velocity of an object, the method including: transmitting an ultrasound signal to an object and receiving an ultrasound echo signal returned from the object determining a velocity of the object based on the ultrasound echo signal displaying a spectral Doppler image showing velocities of the object over time receiving user inputs of selecting an interval within a range of the velocities of the object shown in the spectral Doppler image and adjusting an output volume of an audible sound corresponding to velocities in the selected interval and outputting, based on the adjusted output volume of the audible sound, an audible sound representing the velocities of the object over time.
