An automated teller machine comprising: a main body including a customer service unit where a medium is inserted or a medium is taken out, a deposit/withdrawal unit where a medium is separated and stacked, and a movement path provided between the customer service unit and the deposit/withdrawal unit; a tray configured to transfer the medium while reciprocating on the movement path between the deposit/withdrawal unit and the customer service unit, wherein the tray includes: a tray body that is movable on the movement path between the customer service unit and the deposit/withdrawal unit, the tray body comprising a bottom plate provided on a bottom surface of the tray body; a clamping plate provided at the tray body to be vertically movable for clamping the medium inserted into the tray body; and a clamping lever which, when the tray body is at the customer service unit, is configured to be rotated upward such that the clamping plate is moved upward for generating a medium stacking space between the clamping plate and the bottom plate and to be rotated downward, when the medium is inserted in the medium stacking space, such that the clamping plate clamps the inserted medium by self-weight of the clamping plate for moving the tray body to the deposit/withdrawal unit; characterized in that the main body includes a guide bracket projecting on the movement path of the tray body to guide at least a part of the clamping plate such that the clamping plate is lowered to a preset height along a movement of the tray body while being guided by the guide bracket when the clamping plate is positioned higher than the preset height. a main body including a customer service unit where a medium is inserted or a medium is taken out, a deposit/withdrawal unit where a medium is separated and stacked, and a movement path provided between the customer service unit and the deposit/withdrawal unit; a tray configured to transfer the medium while reciprocating on the movement path between the deposit/withdrawal unit and the customer service unit, wherein the tray includes: a tray body that is movable on the movement path between the customer service unit and the deposit/withdrawal unit, the tray body comprising a bottom plate provided on a bottom surface of the tray body; a clamping plate provided at the tray body to be vertically movable for clamping the medium inserted into the tray body; and a clamping lever which, when the tray body is at the customer service unit, is configured to be rotated upward such that the clamping plate is moved upward for generating a medium stacking space between the clamping plate and the bottom plate and to be rotated downward, when the medium is inserted in the medium stacking space, such that the clamping plate clamps the inserted medium by self-weight of the clamping plate for moving the tray body to the deposit/withdrawal unit; characterized in that the main body includes a guide bracket projecting on the movement path of the tray body to guide at least a part of the clamping plate such that the clamping plate is lowered to a preset height along a movement of the tray body while being guided by the guide bracket when the clamping plate is positioned higher than the preset height. a tray body that is movable on the movement path between the customer service unit and the deposit/withdrawal unit, the tray body comprising a bottom plate provided on a bottom surface of the tray body; a clamping plate provided at the tray body to be vertically movable for clamping the medium inserted into the tray body; and a clamping lever which, when the tray body is at the customer service unit, is configured to be rotated upward such that the clamping plate is moved upward for generating a medium stacking space between the clamping plate and the bottom plate and to be rotated downward, when the medium is inserted in the medium stacking space, such that the clamping plate clamps the inserted medium by self-weight of the clamping plate for moving the tray body to the deposit/withdrawal unit; characterized in that the main body includes a guide bracket projecting on the movement path of the tray body to guide at least a part of the clamping plate such that the clamping plate is lowered to a preset height along a movement of the tray body while being guided by the guide bracket when the clamping plate is positioned higher than the preset height.