1. An apparatus for processing an ultrasonic signal, comprising: IB value calculating means for calculating IB values by extracting RF signals in predetermined time regions respectively from a plurality of RF signals which are produced when an examinee is scanned by an ultrasonic wave; variance value calculating means for calculating a variance value of the IB values calculated by the IB value calculating means; and output means for outputting information based on the variance value calculated by the variance value calculating means.