An apparatus for measuring an amount of urine in a bladder includes a transducer, a switch for selecting one of operational modes, which include a bladder position check mode and a urine amount measurement mode, and a central control unit for operating the apparatus according to the operational mode selected by the switch. The central control unit in the bladder position check mode repeats sequentially predetermined operations until the urine amount measurement mode is selected, the predetermined operations include performing a preliminary scan to a single scan plane related to an aiming direction of the transducer, detecting a center point of the bladder in a ultrasound image, and representing a predetermined mark at the center point of the bladder in the displayed ultrasound image in order to indicate visually a center point of the bladder.
