1. A product search system, comprising: a client terminal, and a server connected to said client terminal via a network, wherein: the server comprises: a product retrieval device which retrieves a product group matching a search query received from the client terminal, and a first communications device which receives the search query from the client terminal and transmits product group information to the client terminal, the product group information being information about the retrieved product group and including images of individual products; and the client terminal comprises: an input device used to input the search query on a display screen of the client terminal, a second communications device which receives the product group information from the server and transmits the search query inputted via the input device to said server, a list control device which displays a list screen of the product group including reduction images of the individual products in a first display area of the display screen based on the received product group information, a selection device used to select one or more desired products on the list screen and deselect a product from the selected products, an information holding device which holds information about the products selected via the selection device until the products are deselected by a user command, and which also holds the information after the information of the product group newly retrieved by the server has been received based on the search query newly inputted by the input device, a selected-image display control device which displays the reduction images of the products selected via the selection device in a third display area of the display screen, a view requesting device used to request to view detailed information about the products selected via the selection device, and a detailed-information display control device which displays detailed information held by the information holding device in a second display area of the display screen when there is a request from the view requesting device to view the detailed information about the products selected via the selection device, the detailed information including images of the products.