The proximate data selecting unit (photographing time distance base proximate data selecting unit) selects, as a proximate photograph, a photograph having a photographing time satisfying constraint on a time distance from a determination time determined in each adjacent photographs block as a time block sandwiched by photographing times of two photographs adjacent to each other in a group of photographs aligned in the order of photographing based on time series photographing time information and outputs proximate data designation information for designating photographing time data of the proximate photograph. The group boundary determining unit detects a change of a photographing disposition in each adjacent photographs block by using photographing time data of a proximate photograph at a determination time in each adjacent photographs block which is designated by the proximate data designation information, thereby determining whether there exists a boundary of a group in each adjacent photographs block.