precision application_number US 56895305 A description hereinafter preferable embodiments of the present invention will be described with reference to the drawings fig1 a is a block diagram showing one exemplary configuration of a receiving section in an ultrasonic diagnostic system according to a first embodiment of the present invention in fig1 a vibrators 1 to 4 are composed of electroacoustic transducers and convert an acoustic echo signal to a received signal the vibrators 1 and 2 constitute a sub array 5 the vibrators 3 and 4 constitute a sub array 6 and the sub arrays 5 and 6 constitute a two dimensional array 7 although only the vibrators 1 to 4 are illustrated in fig1 a actually a number of vibrators are arranged two dimensionally as shown in fig1 b amplifying sections 8 9 respectively output a non inverted output signal and an inverted output signal u2212 of the received signals from the vibrators 1 2 variable amplitude sections 10 11 are connected to the amplifying section 8 via a cross point switch 81 and variable amplitude sections 12 13 are connected to the amplifying section 9 via a cross point switch 91 the output signals of the variable amplitude sections 10 12 are added and the signal thus obtained by addition first signal is supplied to a delay section 14 first delay means furthermore the output signals of the variable amplitude sections 11 13 are added and the signal thus obtained by addition second signal is added to the output signal of the delay section 14 in an adding.