A data space in which a coordinate system is set having, as components, feature data extracted by approximation with respect to frequency spectrums of received ultrasonic waves, when a feature point of a frequency spectrum at a data position is present within a first area in an i-th frame (i is a positive integer) in a display and moves closer to a second area, having a lower priority than the first area, in subsequent (i+1)-th frame; an ultrasonic observation apparatus generates image data by setting a virtual feature point that is far off from the second area as compared to the latest feature point and that is within or around the first area, and by replacing visual information corresponding to the latest feature point in the (i+1)-th frame of the predetermined data position with visual information corresponding to the virtual feature point, and then displays the image data.