An image processing apparatus for diagnostic imaging,which allows easy verification of a spatial position on an arbitrary cross section is provided. An image processing apparatus 1 includes a basic position calculating unit 2 configured to calculate a position of a basic cross section from an image data, an auxiliary position calculating unit 3 configured to calculate a position of an auxiliary cross section, a generating unit 4 configured to generate a basic cross-sectional image using the image data and the position of the basic cross section and generate an auxiliary cross-sectional image using the image data and the position of the auxiliary cross section, a relationship calculating unit 5 configured to calculate information on a positional relationship indicating the relative positional relationship between the position of the basic cross section and the position of the auxiliary cross section, and a combining unit 6 configured to combine the information on the positional relationship with the basic cross-sectional image or the auxiliary cross-sectional image respectively, and a display unit 9 configured to display the combined image.