A display orientation adjustment device for a medical three-dimensional image, comprising: a means for making a display means display a medical three-dimensional image based on medical three-dimensional image data according to a predetermined three-dimensional reference coordinate system (X 0, Y 0, Z 0) a means for making the display means display a reference image to be used as a reference for adjustment of a display orientation of the medical three-dimensional image; an observation direction change command input means for inputting an observation direction change command for changing an observation direction of a display image displayed by the display means; an observation direction changing means for moving the whole display image including the medical three-dimensional image and the reference image according to an observation direction change command input by the observation direction change command input means; a display orientation change command input means for inputting a command for rotatively moving only the medical three-dimensional image of the medical three-dimensional image and the reference image displayed by the display means around a first image reference axis specified among image reference axes of the three-dimensional reference coordinate system (X 0, Y 0, Z 0); a display orientation changing means for rotatively moving only the medical three-dimensional image around the first image reference axis according to a display orientation change command input by the display orientation change command input means; and a first correcting means for correcting medical three-dimensional image data on the three-dimensional reference coordinate system (X 0, Y 0, Z 0) according to the rotative movement of the medical three-dimensional image by the display orientation changing means. a means for making a display means display a medical three-dimensional image based on medical three-dimensional image data according to a predetermined three-dimensional reference coordinate system (X 0, Y 0, Z 0) a means for making the display means display a reference image to be used as a reference for adjustment of a display orientation of the medical three-dimensional image; an observation direction change command input means for inputting an observation direction change command for changing an observation direction of a display image displayed by the display means; an observation direction changing means for moving the whole display image including the medical three-dimensional image and the reference image according to an observation direction change command input by the observation direction change command input means; a display orientation change command input means for inputting a command for rotatively moving only the medical three-dimensional image of the medical three-dimensional image and the reference image displayed by the display means around a first image reference axis specified among image reference axes of the three-dimensional reference coordinate system (X 0, Y 0, Z 0); a display orientation changing means for rotatively moving only the medical three-dimensional image around the first image reference axis according to a display orientation change command input by the display orientation change command input means; and a first correcting means for correcting medical three-dimensional image data on the three-dimensional reference coordinate system (X 0, Y 0, Z 0) according to the rotative movement of the medical three-dimensional image by the display orientation changing means.