Ultrasound diagnostic apparatus

An ultrasound diagnostic apparatus comprising:

• a transmission unit that transmits an ultrasonic wave to a subject via an ultrasound probe;
• a reception unit that receives the ultrasonic wave reflected by the subject via the ultrasound probe;
• and
• an information processing unit that executes processing on a reception signal output from the reception unit,
• wherein the information processing unit
• generates Doppler waveform data based on the reception signal,
• obtains a maximum value, a minimum value, and a reference value of a Doppler waveform line obtained from the Doppler waveform data,
• decides a display range of blood flow velocity indicated by a Doppler waveform based on the maximum value, the minimum value, the reference value, and
• decides the display range by multiplying a larger value of an absolute value of a value obtained by subtracting the reference value from the maximum value and an absolute value of a value obtained by subtracting the reference value from the minimum value by a predetermined scale factor,
• wherein the information processing unit calculates the predetermined scale factor according to values of a scale function for obtaining the predetermined scale factor using an index value, the scale function indicating a curve passing through a plurality of set points or a curve approximated to the curve passing through the plurality of set points,
• the index value is a value indicating a difference between the maximum value and the minimum value, and
• one of the plurality of set points is a point on a coordinate plane in which the index value and the predetermined scale factor are associated with each other.