The first operation portion is configured to be pressed by one hand of a user holding a grip portion. The first button depression portion is configured to move toward a first button of a game controller secured in a compartment, thereby pressing the first button of the game controller secured in the compartment, in response to the pressing operation on the first operation portion. The second operation portion is configured to be pressed by the other hand of the user holding the grip portion. The second button depression portion is configured to move toward a second button of the game controller secured in the compartment, thereby pressing the second button of the game controller secured in the compartment, in response to the pressing operation on the second operation portion.