A display device attachable to a shopping cart, and including a communication module configured to receive information on a specific product from a digital device displaying at least one or more products; a code reader configured to read code information attached to a random product selected from the at least one or more products; a display module; and a controller configured to compare the code information of a product recognized by the code reader with the received information on the specific product, and to control the display module to either display a guide message that the compared code information and the received information are identical or a guide message indicating the compared code information and the received information are not identical.