1. An ultrasonic diagnostic apparatus comprising: a ultrasonic probe; a displacement generation unit configured to displace an inside of a subject and to thus generate a shear wave; a detection unit configured to sequentially transmit a first ultrasonic beam to a plurality of detection positions of the subject from the ultrasonic probe, to receive reflection signals and to detect the displacement at the detection positions by using the received reflection signals, thereby detecting the shear wave, and a control unit configured to calculate a velocity of the shear wave based on an output of the detection unit, thereby outputting hardness information of the subject.