1. An ultrasonic diagnostic apparatus, comprising: a memory configured to store a first ultrasonic image and a second ultrasonic image obtained from ultrasonic scans of an object using an ultrasound probe, wherein each of the first and second ultrasonic images includes an overlap region indicating an identical region of the object; and processing circuitry configured to extract a first block including a plurality of pixels with respect to each position in the overlap region of the first ultrasonic image; extract a second block including a plurality of pixels with respect to each position in the overlap region of the second ultrasonic image; calculate a covariance by using values of pixels constructing each of the first and second blocks with respect to each position; and generate a synthesized image by using the first and second ultrasonic images so that a signal level, is suppressed in accordance with the calculated covariance.