A controller makes a scan part scan a three-dimensional first scanning region so as to acquire volume data in the first scanning region and makes the scan part to consecutively scan a second scanning region that is smaller than the first scanning region and is included in the first scanning region more than once so as to consecutively acquire the volume data in the second scanning region. An image generator generates ultrasound image data in the first scanning region including the second scanning region based on the volume data in the first scanning region. Further, the image generator generates new ultrasound image data by updating the volume data in the second scanning region every time volume data in the second scanning region is acquired. The display controller causes a display to update and causes to display an ultrasound image every time new ultrasound image data is generated.