This invention provides a technology that freely changes the frequency of a reference signal in a digital ultrasonic diagnosis device and makes it possible to conduct various high-quality or high-speed imaging. Reception signals obtained by an ultrasonic element group disposed in an array are digitized in a sampling cycle higher than a Nyquist frequency of the reception signals, and are mixed with reference signal. The mixed signals are then accumulated in a sampling direction, a number of the mixed signals accumulated being equal to a number of a plurality of samples, and are delayed and added by wave reception focusing means. The reference signal serially read out and used from memory means in such a manner as to correspond to the sampling number of the reception signals. A reference signal train acquired from signals, the frequency of which decreases gradually with a lapse of time, from wave transmission, or a reference signal train obtained alternately from two signals having different frequencies, may be stored in advance in memory means.