An opening device for a flap of a vehicle, in particular for a rear flap, pivotable about a horizontal pivot axis on the upper edge of an opening in the vehicle body from a closed position into an open position having a gas-filled spring coupled to the body by the free end of its piston rod at a distance from the pivot axis and coupled to the flap by its pressure tube at a distance from the pivot axis. The gas-filled spring in the exload direction applies a force to the flap in the opening direction. Furthermore, an actuator can act on the flap in the opening direction. The actuator is an energy accumulator which, applies a force to the flap during its opening stroke from the closed position until a relaxed position of the energy accumulator is reached.