An object of the present invention is to enable the convergence of the discharge path length of an ignition plug to a target value irrespective of the condition in a cylinder in an ignition control system for an internal combustion engine equipped the ignition plug that can change the discharge path length. To achieve the object, in the present invention, in an ignition control system for an internal combustion engine equipped with a changing device that changes the path length (or discharge path length) of a spark discharge occurring in the discharge gap of the ignition plug, an actual discharge path length or the path length of a spark discharge that actually occurs in the discharge gap is detected, and the changing device is controlled in such a way that the detected actual discharge path length converges to a target discharge path length.