1. A group information generating system comprising: a group border information generating unit configured to generate histograms of pixel values of plural images corresponding to mutually different cross sections based on a medical image information and generate a border information indicating at least one border of a group when medical images sorted into the group are to be indicated according to the histograms; and a group information generating unit configured to generate a group information according to the border information, the group information meaning a discernment information of the group to which an image indicating information included in the medical image information for indicating one of the medical images is belong.