1. A searching device comprising: a storage section for storing a plurality of pieces of target information concerning a target of a search; a display section capable of displaying first predetermined number of target images corresponding to each of first predetermined number of pieces of target information among the plurality of pieces of target information stored in the storage section; an instructing section for performing an instruction so as to select a certain target image among the first predetermined number of target images displayed on the display section; and a narrowing-down controlling section for performing control so as to narrow down the plurality of pieces of target information stored in the storage section to the first predetermined number of pieces of target information, and so as to display the first predetermined number of target images corresponding to the first predetermined number of pieces of narrowed-down target information, wherein the narrowing-down controlling section comprises: a feature information calculating section for calculating feature information of each target information, the feature information indicating feature of each target information; a coordinate space setting section for setting a predetermined coordinate space based on the feature information calculated by the feature information calculating section; a target information coordinate identifying section for identifying a coordinate of target information corresponding to the target image selected by the instructing section, within the predetermined coordinate space set by the coordinate space setting section; a narrowing-down section for narrowing down a scope of coordinate space within the predetermined coordinate space, the scope including the first predetermined number of pieces of target information corresponding to the first predetermined number of target images to be displayed on the display section; and a narrowed-down target information extracting section for extracting the first predetermined number of pieces of target information corresponding to the first predetermined number of target images to be displayed on the display section for a purpose of narrowing down, among pieces of target information existing within the narrowed-down scope, and the narrowing-down controlling section performs control so as to repeat the identifying the coordinate of the target information by the target information coordinate identifying section, the narrowing down the scope of coordinate space by the narrowing-down section, and the extracting the first predetermined number of pieces of target information by the narrowed-down target information extracting section, at each time that the target image corresponding to the target information is selected by the instructing section.