1. An information display system for displaying information comprising: an information display apparatus which includes an imaging unit; and an information provision apparatus; wherein the information display apparatus comprises: a key information acquiring unit which acquires key information corresponding to a subject in a captured image captured by the imaging unit; and a key information transmitting unit which transmits the key information to the information provision apparatus, wherein the information provision apparatus comprises: a reference image storage unit which stores (i) a plurality of reference images including reference subjects and (ii) actual-size-related scale information of the reference subjects and superimposing information corresponding to the plurality of reference images, respectively; and an information providing unit which selects at least one of the plurality of reference images based on the key information, and which provides to the information display apparatus (i) the at least one selected reference image and (ii) the actual-size-related scale information and the superimposing information corresponding to the at least one selected reference image; and wherein the information display apparatus further comprises: a guide displaying unit which displays actual-size-related guide information based on (i) the actual-size-related scale information corresponding to the at least one selected reference image, and (ii) actual-size-related scale information of the captured image; an image matching unit which matches the subject included in the captured image with the at least one selected reference image in accordance with the displayed actual-size-related guide information; and a superimposed displaying unit which superimposes and displays the superimposing information corresponding to the at least one selected reference image based on a matching result matched by the image matching unit on the captured image.