A diagnosis apparatus in which a lesion in the large intestine can be diagnosed with high precision by detecting pits is provided. A three-dimensional optical tomographic image is obtained by the configuration of an apparatus using an endoscope and an optical probe, images in X-Y planes perpendicular to the depth direction of a living body tissue are cut out at a plurality of depth positions, based on the three-dimensional tomographic image data, and a pit pattern shape highlighted image is generated from their average image to perform diagnostic support.