A server 2 includes an extraction unit 21, an analysis unit 22, a first estimating unit 24, an information acquisition unit 25 and a second estimating unit 26. The extraction unit 21 extracts an image area for each article. The analysis unit 22 analyzes the image area to acquire analysis information. The first estimating unit 24 narrows down candidates estimated to correspond to the article in the image area based on the analysis information. When the candidates were able to be narrowed down, the information acquisition unit 25 acquires additional information additional information of a reference article. The second estimating unit 26 attempts a narrowing process based on the additional information of the reference article in addition to the analysis information, for the image area including a spine, which is an image area in which candidates were unable to be narrowed down.