A bracket device includes a bracket, at least one mounting member mounted on the bracket, a locking member movable with respect to the bracket, and a fool-proofing member to be located at a first position or a second position with respect to the bracket. When the bracket is at a first mounting angle, the fool-proofing member is located at the first position and is unable to block the locking member from moving with respect to the bracket. When the bracket is flipped from the first mounting angle to a second mounting angle, the fool-proofing member is displaced from the first position to the second position and ends up blocking the moving path of the locking member with respect to the bracket.