To provide a diagnosis assisting apparatus capable of easily acquiring, on a diagnostic screen of tubular tissue, a positional relationship between a curved cutting surface and tubular tissue shown in a CPR image.

A tubular tissue region 5 showing tubular tissue is extracted from volume data acquired by photographing, and a core line CL of the tubular tissue is extracted to form the CPR image including a longitudinal section of the tubular tissue region including the core line CL. The longitudinal section is acquired from a CPR image forming means, and a pseudo three-dimensional image 31 including an index SV representing the longitudinal section acquired in the extracted tubular tissue 5, as well as the tubular section 5, is formed based on the volume data and displayed.