A center-of-gravity detection system includes a vehicle capable of carrying cargo and adapted to be towed by a towing vehicle, a shake detector configured to detect shakes in the directions of the self-weight and width of the towed vehicle during travel of the towed vehicle, and an arithmetic unit. The arithmetic unit is configured to derive, based upon physical quantities that correlate with the shakes, the location of the center of gravity, in three-dimensional space, of the towed vehicle.