1. An ultrasonic imaging apparatus comprising: a transducer that transmits or receives ultrasonic waves to or from a subject; an image data production unit that produces a plurality of image data items on the basis of a plurality of receiving signals due to the transducer; a frame memory that preserves the image data items; a temporal change measurement unit that measures a temporal change in brightness of each of pixels of image data; an image construction unit that constructs a color map on the basis of the results of measurement by the temporal change measurement unit; an input unit that inputs display-item information concerning the color map; and a pixel detection unit that extracts pixels from the color map so as to construct an extractive image.