An example supporting device supports two game controllers. The supporting device includes a support section and a main section connected to the support section. The support section includes a first slide member and a second slide member. The first slide member is provided in an area of the support section toward a first side in a predetermined direction, and the second slide member is provided in an area toward a second side. The slide members are capable of slidably engaging with rail members of the respective game controllers in a predetermined slide direction. The first slide member includes a first terminal provided on a first opposing surface. The second slide member includes a second terminal provided on a second opposing surface. The main section includes a first grip portion for being gripped by a user, and a second grip portion for being gripped by the user.