An example game controller is removably attachable to a main unit. The game controller includes an operation section and a controller-side slide member. The controller-side slide member protrudes from a first surface of the game controller and is configured to slidably engage with the main unit-side slide member in a slide direction. The controller-side slide member has a first end and a second end in the slide direction, and the game controller is configured to be attached to the main unit by inserting the controller-side slide member into the main unit-side slide member at least from the first end. The game controller includes a stop member. The stop member is configured to protrude from the first surface of the game controller or from a side surface of the controller-side slide member, which side surface is substantially perpendicular to the first surface.