To accurately answer a question about what is imaged and reduce user's load by enabling information retrieval based on the image.

A terminal device 3 transmits retrieval information including an image taking an unkown object and attached information on the image to a server 2. In the server 2, when retrieval information is input, an information retrieval device selection part 25 selects an information retrieval device 4 as a transmit object for retrieval information from a plurality of information retrieval devices 4 by referring to reference information 251 according to the attached information. The reference information stores information related to the speciality or the like of each information retrieval device 4, and the information retrieval device 25 selects the information retrieval device 4 in consideration of the speciality of each information retrieval device 4. The retrieval information is transmitted to the selected information retrieval device 4, whereby the information retrieval device 4 requested to perform information retrieval performs information retrieval (retrieval for answering a question about what is photographed in the image) by an image.