An ultrasonic diagnostic system includes electroacoustic conversion means in which a plurality of sub-arrays, each composed of a plurality of electroacoustic transducers, are arranged at least two-dimensionally, sub-beam formers that are provided on the sub-array basis, and a main beam former for subjecting signals output from the sub-beam formers to delay addition. Each sub-beam former generates signals having polarities different from each other from each of received signals from the electroacoustic transducers in the sub-array, obtains a first signal and a second signal that are obtained by controlling amplitudes of signals having different polarities generated from the received signals from the electroacoustic transducers in the sub-array, followed by adding, imparts a delay time difference corresponding to a quarter of one period of the received signal between the first signal and the second signal by first delay means composed of a capacitor memory provided inside, and adds the first signal and the second signal to which the delay time difference is imparted. The ultrasonic diagnostic system with this configuration is capable of phasing a received signal with high precision.