An ultrasonic wave beam former including: a ultrasonic wave probe (1) equipped with a plurality of transducers (2) for converting a ultrasonic wave signal to an electric signal for effecting a dynamic focus by multiplying each channel signal as an output signal from each of the transducers (2) by a reference wave signal having the phase which is dynamically adjusted for each channel, and adding together each after-multiplication signal after the multiplication through a delay line (3), characterized in that at least two kinds of reference signals having mutually different frequencies are provided for each of the channels and at least two multipliers (10) are also provided;each of the reference signals is constituted so as to receive an ultrasonic wave signal from a direction differenct from others and have a phase angle (.theta. (i)) adjusted so as to effect a dynamic focus;the after-multiplication signal from each of the multipliers (10) for each channel is supplied to the delay line (3); andthe superposed after-multiplication channel signal for each channel is added to one another through the delay line (3) and is subjected to a frequency separation by a filter (19) adapted to correspond to the frequency of the reference signal.