A side impact cushion device of a motor vehicle contains at least one impact cushion which can be inflated by a gas generator. The impact cushion in an installation state has an upper portion, a central portion and a lower portion. In this case, the upper portion is arranged substantially horizontally in a deployed state, the central portion is formed in the form of a shell surface of a rotationally symmetrical, developable body, the lower portion can be supported on an upper side of an armrest and a rotational axis of the rotationally symmetrical body is oriented vertically in the deployed state.