Abstract: In an ultrasonic diagnostic apparatus which uses at least part of an array of a plurality of ultrasonic vibrators as an aperture for ultrasonic beam formation, sends ultrasonic waves into an object, receives echoes from the object, delays the output echo signals of a plurality of vibrators participating in receiving the echoes by a given quantity, adds up the delayed echo signals for echo beam forming, and forms a picture of an internal structure of the object by using the signals obtained by echo beam forming, the echo beam forming is characterized by forming a plurality of partial apertures in an aperture of an array of ultrasonic vibrators, delaying the echo signals provided by groups of vibrators included in the plurality of partial apertures by a given quantity determined so that a plurality of echo beams having a common focal point are formed, adding up the delayed echo signals of each group, detecting the respective sums of the delayed echo signals of the groups, and adding up the respective detected s