An ultrasonic diagnostic apparatus comprising: an ultrasonic probe; a tomographic image constructing means for constructing a tomographic image based on RF frame data of the tomographic region of an object to be examined via the ultrasonic probe; an elasticity information calculating means for obtaining strain or elasticity modulus in the tomographic region based on the RF signal frame data; an elastic image constructing means for generating an elastic image in the tomographic region based on the strain or the elasticity modulus obtained in the elasticity information calculating means; a display means for displaying the tomographic image and/or the elastic image; and further comprising a compression bag placed on an ultrasonic wave transmitting/receiving surface of the ultrasonic probe in which liquid is to be filled; a liquid charging/discharging means for expanding or deflating the compression bag by charging/discharging the liquid to/from the compression bag; a pressure measuring means for measuring the pressure of the liquid filled in the compression bag; and a pressure calculating means for calculating the pressure of an ultrasonic scanning region of the object where the compression bag is applied, wherein the elasticity information calculating means is configured to calculate elasticity modulus using the calculated pressure information of the pressure calculating means, characterized by a flow volume measuring means for measuring the inflow/outflow volume of the liquid in the compression bag, wherein the pressure calculating means is configured to calculate the pressure of the ultrasonic scanning region of the object to which the compression bag is applied based on the pressure information measured in the pressure measuring means and an inflow/outflow volume of the liquid measured in the flow volume measuring means. an ultrasonic probe; a tomographic image constructing means for constructing a tomographic image based on RF frame data of the tomographic region of an object to be examined via the ultrasonic probe; an elasticity information calculating means for obtaining strain or elasticity modulus in the tomographic region based on the RF signal frame data; an elastic image constructing means for generating an elastic image in the tomographic region based on the strain or the elasticity modulus obtained in the elasticity information calculating means; a display means for displaying the tomographic image and/or the elastic image; and further comprising a compression bag placed on an ultrasonic wave transmitting/receiving surface of the ultrasonic probe in which liquid is to be filled; a liquid charging/discharging means for expanding or deflating the compression bag by charging/discharging the liquid to/from the compression bag; a pressure measuring means for measuring the pressure of the liquid filled in the compression bag; and a pressure calculating means for calculating the pressure of an ultrasonic scanning region of the object where the compression bag is applied, wherein the elasticity information calculating means is configured to calculate elasticity modulus using the calculated pressure information of the pressure calculating means, characterized by a flow volume measuring means for measuring the inflow/outflow volume of the liquid in the compression bag, wherein the pressure calculating means is configured to calculate the pressure of the ultrasonic scanning region of the object to which the compression bag is applied based on the pressure information measured in the pressure measuring means and an inflow/outflow volume of the liquid measured in the flow volume measuring means.