The ultrasonic diagnosis apparatus according to the embodiments transmits ultrasonic waves to a subject, generates an ultrasound image based on the signals received from the subject, and comprises sub arrays, a main array, an aperture diameter setting part, and a delay pattern setting part. The sub arrays consist of a plurality of ultrasound transducers that are two-dimensionally disposed, and have a fixed delay pattern during a single receiving period. The main array consists of sub arrays. The aperture diameter setting part sets the aperture diameter of the main array. The delay pattern setting part changes the delay pattern for each of the sub arrays depending on the aperture diameter.
