1. An ultrasonic diagnostic apparatus comprising: a transmitter that transmits ultrasonic waves into an object; a receiver that receives a signal from the object; and a processor programmed to: produce a sectional image for each of a plurality of arbitrary cross sections of the object based on the received signal; process the signal to produce a two-dimensional elasticity image of an elasticity value representing elasticity for each of the plurality of arbitrary cross sections; process the signal to produce a three-dimensional image of a predetermined part of the object; process the signal to produce a three-dimensional elasticity image of the elasticity value of the predetermined part of the object; receive an operation of setting a first combination ratio from an operator; receive an operation of setting a second combination ratio from an operator; add the sectional image and the two-dimensional elasticity image of each of the plurality of arbitrary cross sections to produce a plurality of arbitrary cross-section combined images, at least one of the sectional images and the two-dimensional elasticity images being combined at the first combination ratio; add the three-dimensional image and the three-dimensional elasticity image at the second combination ratio to produce a three-dimensional combined image, the second combination ratio being different from the first combination ratio; and display the arbitrary cross-section combined images and the three-dimensional combined image side by side on a display, so as to simultaneously display an external form of the object with hardness information in the three-dimensional combined image and an inside of the object with hardness information in the arbitrary cross-section combined images.