An auxiliary device for sparkplug ignition is provided having a case, and provided therein, electrolytic capacitors connected in parallel between ground terminals and positive terminals of the primary coils of the ignition coils, which are connected to sparkplugs in a direct ignition system. Diodes, which are connected in parallel, are provided in the reverse direction, between the ground terminals and the positive terminals on the primary coils. The case is fitted with a connector that connects to a dedicated harness. The back electromotive force generated in the primary side coils L1 to L4 of the ignition coils of each sparkplug is absorbed, so as to adjust the primary side current, allowing for generation of stabilized high voltage on the secondary coil side, and producing highly efficient sparkplug ignition.
