An apparatus for measuring an amount of urine in a bladder using ultrasonic signals includes: a transducer a switch for selecting one of operational modes, which include a preliminary scan mode and a scan mode a transducer drive unit for driving the transducer and a central control unit for operating according to the operational mode to provide an amount of urine in the bladder. The central control unit in the preliminary scan mode performs a preliminary scan to obtain ultrasonic signals for a single scan plane from the transducer, generates a 2-D B-mode ultrasonic image using the ultrasonic signals obtained in the preliminary scan, trace an outline of a bladder on the 2-D B-mode ultrasonic image, generates an aiming image, estimate a volume of the bladder, and displays the 2-D B-mode ultrasonic image represented the traced outline, the aiming image and the estimated value to the display unit.
