An ultrasonic diagnosing apparatus includes: a transducer array 1 composed of arrayed transducer elements T1 to T6 for transmitting ultrasound; driving circuits D1A to D6A each provided for transmission channels for driving each of the transducer elements; a transmission trigger generator 2 for generating a trigger pulse for controlling each of the driving circuits; a parallel reception beam former 3 for processing reception signals from the transducer elements; a signal processor 4 for processing an output signal of the parallel reception beam former; and a control unit 5 for controlling the transmission trigger generator, the parallel reception beam former and the signal processor. The transmission trigger generator controls the width of the trigger pulse independently for each of the transmission channels to cause the driving circuit to output a driving pulse approximating a predetermined weighting value assigned to an output amplitude of each of the transmission channels in a transmission aperture of the transducer array. A circuit for forming a trapezoidal transmission beam for increasing a data acquisition rate by using parallel reception beams can be configured at low cost by using pulse amplifiers.