1. An article recognition apparatus comprising: an image acquisition unit configured to acquire a photographed image captured by photographing a photography range including a range in which all articles to be recognized are disposed; a recognition unit configured to detect all of identification patterns for identifying the articles in the photographed image, and to recognize each of the articles by each of the detected identification patterns; a region detection unit configured to detect image regions of the articles in the photographed image, and to determine article region information from the detected image regions of the articles; a storage unit configured to store, with respect to each of the articles that are objects of recognition by the recognition unit, article information including a reference value for the article region information which the region detection unit determines from the image regions of the articles; and a determination unit configured to determine that an unrecognized article exists, if the reference value for the article region information of each article which the recognition unit recognized does not match with the article region information which the region detection unit determined from the image regions of the articles in the photographed image.