To provide a medical image displaying device with which a rotary shaft of a projection can be made to coincide with the body axis by a simple operation of an operator to provide an effective projection image for a diagnosis when the projection processing of a three-dimensional image data acquired by a photographing apparatus is performed.

A projection image or a tomogram produced from the three-dimensional data of an examinee is displayed and a mark which indicates a rotary shaft when projections in two or more directions are performed is displayed on a GUI. When the operator drags the mark displayed on the GUI to make the same coincide with the body axis of the examinee, the amount of movement (the amount of rotation) of the mark is read out by an image processing section and correction (rotational transform) of the coordinate of the three-dimensional data is performed. The images which are projected in the two or more directions making the corrected rotary shaft the center do not have fluctuations of positions of tissues so that the images are easy to diagnose.