An automated teller machine comprises a main body; a deposit/withdrawal unit provided at one side in the main body and configured to separate and stack a medium; a customer service unit provided at a front side of the main body and configured to receive a medium from a user; and a tray unit configured to transfer a medium between the deposit/withdrawal unit and the customer service unit while reciprocating therebetween. The deposit/withdrawal unit includes a bill stopper that is rotatably provided to open and close an opening of the deposit/withdrawal unit through which the tray unit passes; and a link unit configured to open and close the bill stopper by providing a rotational force to the bill stopper.