1. An image processing apparatus comprising: an image creating unit that acquires three-dimensional histology information about tissue inside a subject and three-dimensional fluid information about fluid moving inside the subject both of which are created based on a reflection wave of an ultrasonic wave transmitted to the inside of the subject, creates three-dimensional particle information converted from the three-dimensional fluid information by arranging a plurality of particles in three dimensions in a scattered manner in an area in which the fluid is present in the three-dimensional fluid information, and creates a composite image based on created three-dimensional particle information and the three-dimensional histology information; and a display control unit that controls display of the composite image created by the image creating unit so as to be displayed onto a predetermined display unit.