Information processing system, information processing method, information processing device, as well as control method and control program therefor

[Problem] To relieve traffic congestion by actively reducing the amount of traveling a user needs to do in order to purchase a product. [Solution] Provided is a product purchase request acquiring unit for acquiring the location of a user and information on a product purchase request from the user; a product purchase information notification unit for connecting, via a network, to a communication terminal at a retail store whose distance from the location of the user is shorter than a first threshold value, and for notifying the terminal of information related to the product purchase request from the user; and a product purchase guide unit for receiving, via the network, inventory information on the product at the retail store, and for providing to a communication terminal of the user, via the network, guidance to the retail store to purchase the product.