An example game controller is removably attachable to a main unit having a main unit-side slide member and configured to execute a game process. The game controller having a front surface and at least first and second side surfaces relative to the front surface. The game controller includes a controller-side slide member. The controller-side slide member protrudes from the second side surface and is configured for slidably engaging with the main unit-side slide member in a slide direction. The controller-side slide member includes a lower surface and an upper surface. The lower surface extends from the first end to the second end of the controller-side slide member in a direction substantially perpendicular to the slide direction. The game controller includes a first operation control. The first operation control is provided on the lower surface.