An ultrasonic diagnostic apparatus comprising: an ultrasonic intra-luminal probe for transmitting/receiving ultrasonic waves to/from an object to be examined; pressing means for adding pressure to biological tissues of the object; transmission means for transmitting ultrasonic waves to the biological tissues by the ultrasonic probe; reception means for receiving the reflected echo signals generated from the object by the ultrasonic probe; strain information calculating means for obtaining strain distribution of biological tissues based on a pair of frame data acquired at different times received by the reception means; strain image construction means for constructing a strain image based on the strain distribution obtained by the strain information calculating means; and display means for displaying the strain image, characterized in further comprising strain distribution correcting means for correcting the strain distribution by a strain distribution correcting function being set in accordance with the pressing condition by the pressing means, wherein the pressing means is a balloon which is attached to the ultrasonic probe, and which is expanded or contracted by charging water thereto or discharging water therefrom, respectively; the balloon is a spherical-shaped balloon or a balloon having a cylindrical shaped membrane; and if the balloon is the spherical-shaped balloon, the strain distribution correcting function is defined as (r/rO) 2, and if the balloon is the balloon having the cylindrical-shaped membrane, the strain distribution correction function is defined as (r/rO), where rO is a curvature radius of the balloon in its initial state and r is a radial coordinate of a measurement point in the object. an ultrasonic intra-luminal probe for transmitting/receiving ultrasonic waves to/from an object to be examined; pressing means for adding pressure to biological tissues of the object; transmission means for transmitting ultrasonic waves to the biological tissues by the ultrasonic probe; reception means for receiving the reflected echo signals generated from the object by the ultrasonic probe; strain information calculating means for obtaining strain distribution of biological tissues based on a pair of frame data acquired at different times received by the reception means; strain image construction means for constructing a strain image based on the strain distribution obtained by the strain information calculating means; and display means for displaying the strain image, characterized in further comprising strain distribution correcting means for correcting the strain distribution by a strain distribution correcting function being set in accordance with the pressing condition by the pressing means, wherein the pressing means is a balloon which is attached to the ultrasonic probe, and which is expanded or contracted by charging water thereto or discharging water therefrom, respectively; the balloon is a spherical-shaped balloon or a balloon having a cylindrical shaped membrane; and if the balloon is the spherical-shaped balloon, the strain distribution correcting function is defined as (r/rO) 2, and if the balloon is the balloon having the cylindrical-shaped membrane, the strain distribution correction function is defined as (r/rO), where rO is a curvature radius of the balloon in its initial state and r is a radial coordinate of a measurement point in the object.