An accessory device for use with a first game controller including at least a first button and a second button and a protruding portion on a rear surface thereof, and a second game controller including at least a third button and a fourth button and a protruding portion on a rear surface thereof, the second game controller having a different shape from that of the first game controller, the accessory device comprising: a compartment configured to allow both of the first game controller and the second game controller to be removably attached thereto, one at a time, and configured to removably secure both of the first game controller and the second game controller therein, one at a time; a first movable portion; and a second movable portion, the compartment including: a first engagement portion located on a first side in a predetermined direction and configured to engage with the protruding portion of the first game controller; and a second engagement portion located on a second side in the predetermined direction and configured to engage with the protruding portion of the second game controller, the first movable portion including: a first operation portion; and a first button depression portion configured to press the first button of the first game controller when the protruding portion of the first game controller is in engagement with the first engagement portion and configured to press the third button of the second game controller when the protruding portion of the second game controller is in engagement with the second engagement portion, the second movable portion including: a second operation portion; and a second button depression portion configured to press the second button of the first game controller when the protruding portion of the first game controller is in engagement with the first engagement portion and configured to press the fourth button of the second game controller when the protruding portion of the second game controller is in engagement with the second engagement portion. a compartment configured to allow both of the first game controller and the second game controller to be removably attached thereto, one at a time, and configured to removably secure both of the first game controller and the second game controller therein, one at a time; a first movable portion; and a second movable portion, the compartment including: a first engagement portion located on a first side in a predetermined direction and configured to engage with the protruding portion of the first game controller; and a second engagement portion located on a second side in the predetermined direction and configured to engage with the protruding portion of the second game controller, a first engagement portion located on a first side in a predetermined direction and configured to engage with the protruding portion of the first game controller; and a second engagement portion located on a second side in the predetermined direction and configured to engage with the protruding portion of the second game controller, the first movable portion including: a first operation portion; and a first button depression portion configured to press the first button of the first game controller when the protruding portion of the first game controller is in engagement with the first engagement portion and configured to press the third button of the second game controller when the protruding portion of the second game controller is in engagement with the second engagement portion, a first operation portion; and a first button depression portion configured to press the first button of the first game controller when the protruding portion of the first game controller is in engagement with the first engagement portion and configured to press the third button of the second game controller when the protruding portion of the second game controller is in engagement with the second engagement portion, the second movable portion including: a second operation portion; and a second button depression portion configured to press the second button of the first game controller when the protruding portion of the first game controller is in engagement with the first engagement portion and configured to press the fourth button of the second game controller when the protruding portion of the second game controller is in engagement with the second engagement portion. a second operation portion; and a second button depression portion configured to press the second button of the first game controller when the protruding portion of the first game controller is in engagement with the first engagement portion and configured to press the fourth button of the second game controller when the protruding portion of the second game controller is in engagement with the second engagement portion.