A mode selector is provided, capable of selecting one of a measurement mode of measuring urine volume while an ultrasound probe is placed at a certain measurement position on the stomach of a measurement subject, and a positioning mode is provided, of measuring urine volume while moving the ultrasound probe to a plurality of tentative measurement positions on the stomach to determine the measurement position suitable for placing the ultrasound probe in the measurement mode. An index value memory is included that stores a maximum value among urine volumes at the plurality of tentative measurement positions, calculated by the arithmetic unit, while the positioning mode is being selected, and/or an allowance value determined on the basis of the maximum value. The maximum value and/or the allowance value is displayed, on a graph on a display unit, as a positioning index value for positioning the ultrasound probe.
