1. An ultrasonic diagnostic apparatus, comprising: an ultrasonic probe; a position sensor attached to the ultrasonic probe, and configured to generate a positional data signal pertaining to a spatial coordinate position of the ultrasonic probe and a scanning direction/orientation; and processing circuitry configured to control the ultrasonic probe to execute echocardiography and to generate an echocardiographic image including an aorta and a bifurcated artery bifurcating from the aorta, acquire a heart area image from a storage prospectively storing the heart area image, extract an artery region based on the heart area image, identify a flap region based on the artery region, synthesize information on the flap region by using the artery region to generate a first synthesized image, the flap region being a region of a flap caused by intimal dissection, and the information indicating the flap region, perform processing to align an imaging region in the echocardiography on the heart area image based on the positional data signal, and synthesize additional information indicating the imaging region processed for alignment onto the first synthesized image to generate and display a second synthesized image.