The present invention provides an apparatus for displaying a two-dimensional cross-sectional image of an arbitrary base plane which matches to the subject's head without creating extra labor to the operator even when the subject's head is asymmetrical. The apparatus is connected to a display unit for displaying a cross-sectional image of a head. The apparatus comprising: a conversion parameter obtaining unit for obtaining a conversion parameter indicating a difference in shape between a standard head and a subject's head based on a volume data; a subject base plane generating unit for generating an anatomical base plane of the subject's head based on the conversion parameter and an anatomical base plane of the standard head; and a cross-sectional reconstruction unit for generating a cross-sectional image of the anatomical base plane of the subject's head based on the volume data of the subject's head and displaying said cross-sectional image on the display unit.