1. An ultrasound diagnostic device comprising, an ultrasound probe which emits an ultrasound wave and receives a reflected wave of the ultrasound wave, a first position detector which detects a position of the ultrasound probe, an ultrasound image generator which generates an ultrasound image by using a reflected echo signal based on the reflected wave, a reference image generator which generates plural reference images of an arbitrary cross section by using three-dimensional volume data of a test object and displays an ultrasound probe mark indicating the position of the ultrasound probe in a superimposed manner on the reference image, and an image processor which displays the ultrasound image and the reference image on a display, wherein the reference image generator: indicates a position of another reference image by displaying a line on each of the plural reference images, and draws an area representing a shape of the ultrasound probe when an ultrasound emitting plane of the ultrasound probe exists within a reference image of the plural reference images, and draws only an outline of the probe when the ultrasound emitting plane of the ultrasound probe does not exist within the reference image.